Crop Profile for Peanuts in Florida
Prepared December 4, 2000
General Production Information
Peanut is adapted to all portions of northern Florida (6). The vast majority of peanut is produced in the panhandle and north-central regions of the state. Jackson, Santa Rosa, Levy, Walton, Suwannee, Holmes, Marion, Calhoun, and Columbia counties account for approximately 90 percent of the state’s peanut production (1,5).
Peanut, also called goober, pindar, groundnut and earthnut, is a legume and a member of the pea family. It is a perennial herb, which is actually grown as an annual for production. Seeds are planted in the spring, beginning about mid-March in north-central Florida and April 1 in north Florida, whenever the minimum soil temperature at the 4-inch depth is 65 degrees F or more for three consecutive days and a cold front is not expected soon after planting. Planting continues through May, and in some years into June if dry weather persists. Many factors affect the dates, rates, and methods of planting of Florida peanuts. Seeds are planted 2 to 4 inches apart, 2 to 3 inches deep, in rows 24 to 36 inches apart, depending on the variety to be planted (3,6,7,12). Twin rows, where two rows about 7 inches apart replace a single row, are becoming popular. If runner or Spanish peanut varieties are planted, seeding rates are 50 to 120 pounds per acre, whereas Virginia peanuts will be planted at rates in the 90 to 135 pounds per acre (7,14). Approximately 10 days after planting the crop emerges (cracking), and flowers appear 30 to 45 days after planting. The first pegs form and enter the soil a few days after bloom. Pod development then occurs. The plant continues to flower and set fruit in cycles dependent on the environment and fruit load throughout the season. Around 60 to 70 days after planting, the crop will reach full canopy closure. The maturity date varies depending on peanut type and cultivation but ranges between 100 to 160 days after planting. Commercial peanut harvest is done mechanically, with the harvest date determined by balancing weight gains and losses between mature and immature fruit. Peanut is occasionally planted later in the planting-window season, because of the lack of rainfall during some spring seasons. Late planted peanut crops typically require more pesticides to generate typical yields (3,14).
At harvest, producers dig the crop by inverting the plant’s vines on top of the soil, where it cures for about three days before combining (threshing). After combining, pods are dried with forced air in trailers before being graded and sold. Because of its underground fruit development, peanut production requires special harvesting equipment that is not used for any other crop (3,9).
Peanut is grown in soil that has a target pH of 6.0. Nitrogen fertilizers are not necessary because the crop is a legume and therefore capable of fixing nitrogen within its root nodules. However, many growers apply a small amount of nitrogen to stimulate early growth. Depending on the soil fertility, 40 to 100 pounds per acre each of phosphorous (P2O5) and potassium (K2O) fertilizer are applied annually. If peanut is grown for seed, or they are Virginia type, or soil tests indicate a need, gypsum (CaSO4) is applied broadcast at early flowering to compensate for any calcium deficiencies. The rate of dry gypsum, when applied in a band over the row, is 400 pounds per acre and 800 pounds per acre for Virginia types. Boron is applied at 0.75 pounds per acre in the fertilizer or 0.5 pounds of boron per acre as a foliar spray, usually with the first fungicide application (6,10,11).
Before the crop is purchased from the grower, it must be graded according to industry standards and inspected by licensed government personnel from the USDA Federal State Inspection Service for the fungus, Aspergillus flavus or A. parasiticus , sources of aflatoxin. In fact, peanut is one of the three crops with the highest potential for invasion by Aspergillus species, the other crops are corn and cottonseed. Peanut seed can be colonized by Aspergillus while in the ground in the seedling stage, before digging, during curing and drying in windrows, and in storage. Damage to the pericarp of the peanut induced by insects, drought, hail, frost, or mechanical harvest favors Aspergillus invasion. Insect damage can exacerbate the aflatoxin problem, so precise insect and disease management is imperative. Each wagon load of peanut is inspected and these will be condemned to the oil market if even one kernel in the grade sample is found to contain the Aspergillus mold. Inspections for aflatoxin also are conducted during the shelling process (3,8).
Insect pests of peanut are quite widespread across the production area and include: thrips, fall armyworms, cutworms, corn earworms, lesser cornstalk borers, wireworms, white grubs, leafhoppers, spider mites, aphids, rednecked peanut worms, whiteflies, three-cornered alfalfa hoppers, velvetbean caterpillars, and whitefringed beetle larvae. Insect problems vary during the growing season and from one season to the next because of varying factors such as weather and cultural practices.
Weekly scouting of each individual peanut field is recommended for insect pests. Inspections consist of thoroughly inspecting the vines, including both upper and lower leaf surfaces. Research has defined economic management treatment thresholds for certain insect pests, to identify the amount of damage a peanut plant can withstand without a yield loss. For armyworms, corn earworms or other foliage-feeding worm pests:
- Early season: 3 to 4/row-foot before plants meet in the middle. Then 4 to 5/row-foot after the plants reach in the middle.
- Late season: 5 to 6/row-foot once peanuts have completely covered the middles.
For cutworms, defoliation appears to be the best measure of damage levels. When approximately 20 percent defoliation is reached, management treatment are necessary. For peg and pod feeders such as lesser cornstalk borers and corn rootworms, treatment is necessary when the caterpillars or rootworms are found infesting 10 percent of the plants before pegging and 15 percent after pegging (15,16).
Aphids. Aphids are soft-bodied, sucking insects about 1/8 of an inch long. They are not generally a problem on peanut but in large numbers can cause considerable damage through reduction of plant fluids. Aphids are vectors for peanut mottle, peanut stripe, and peanut stunt viruses.
Corn Earworms. The corn earworm is a general feeder found on peanut and other crops such as corn, cotton, soybean, tobacco and tomato. They can develop into large infestations. These caterpillars vary in color from light green to pink to nearly black but are generally lighter on the undersurface of their body. When disturbed, they will curl their bodies up very tight. Small corn earworms are easier to control than the larger ones so it is important to check fields thoroughly and regularly.
Cutworms. Cutworms are stout and dark colored. During the day they stay just below the soil surface, under trash or in soil cracks. Most damage is done at night when they climb the plants and feed on the foliage; however, they also will cut plants off at the soil surface. The cutworms also will feed on exposed peanuts that have been dug. Care needs to be taken in inspection of cutworm populations just before harvest since as soon as the vines are plowed, the worms will leave the drying foliage and begin feeding on the pods.
Armyworms. The stripes and coloration of the fall armyworm are highly variable; however, they can generally be identified by a white inverted "Y" mark in front of the head. Beet armyworms can be identified by a black spot on each side of the body just behind the head. The adult moth lays eggs in a "fuzzy cluster" and when they hatch the caterpillars move and feed together. Often large numbers congregate and move along together feeding on foliage; consequently, they are called armyworms. They often attack the vines early in the season and feed on developing buds. This type feeding gives a ragged appearance when the leaves expand.
Leafhoppers. Leafhoppers are small green or brownish wedge-shaped insects sometimes called sharpshooters. They have piercing-sucking mouthparts and damage peanut by sucking sap from the leaves and buds causing leaf tips to turn yellowish-white or fringes of the leaf to turn brown (called "hopper burn").
Lesser Cornstalk Borers. The lesser cornstalk borer is small and slender with alternating green and brown bands on its body. It lives in a silken tube just below the soil surface and bores into and tunnels up the stem. Lesser cornstalk borers frequently attack seedlings emerging from the ground or shortly thereafter. It is an erratic pest with outbreaks and plant damage usually occurring during dry periods on sandy soils. The worm also can be a severe problem from pegging time until harvest. Damage can be reduced significantly by keeping the land free of weeds and grass for several weeks before planting. To inspect for the lesser cornstalk borer, it is necessary to carefully dig the peanut plant with a trowel, small shovel or other instrument. The delicate sand-like silk webbing tubes are often left in the soil if the plant is not carefully removed. If the above precautions are not observed, the grower will often overlook this dangerous pest. Earlier planting may help prevent late season losses.
Rednecked Peanut Worms. The rednecked peanut worm is a small, white-colored larvae with a brown head and a red band just behind the head in the neck region, hence its name. They are 3/8 to 1/2 inch in length and feed in the buds of the plant. They do not regularly occur but can be difficult to manage.
Corn Rootworms. The southern corn rootworm damages peanut by feeding on the pegs and pods in the soil. These pests tend to be a problem more often in damp weather and on heavier type soils, however, it can occur in sandy soils. The adults of the corn rootworm beetle are greenish-yellow in color, about 1/4 to 3/8 of an inch long and have 12 irregular black spots on their backs. The damage to peanut, however, is caused by the whitish-clear tender looking larvae about 3/8 inch long. The larvae appears two "headed" since both head and rear ends have a brown-like spot resembling the head of a worm. Management of this pest also can be quite frustrating because its underground feeding. Once it is detected, it is virtually impossible to use any type of rescue treatment effectively. Therefore, producers generally rely upon preventive applications of granular formulations of insecticides just before anticipated egg hatch.
Spider Mites. Spider mites, about 1/60 of an inch long, are not insects but closely related organisms that damage peanut by sucking fluid from the leaves causing them to turn yellow and die. They are not a common problem but may appear from time to time and can cause severe damage. Mites are particularly troublesome in dry weather and populations generally initiate around fences, trees, field margins or other obstacles in the field. They prefer healthy and vigorous plants to feed upon. Problems with spider mites can be enhanced when certain foliar pesticides are used.
Whiteflies. The sweetpotato whitefly, Bemisia tabaci (Gennadius), was first found in Florida about 1900. The adult is a moth-like insect approximately 0.8 mm (1/32") long. It inhabits and feeds on the undersurfaces of leaves by penetrating the tissue and removing plant sap with its piercing-sucking mouthparts. The insect’s snow-white color is attributed to the secretion of wax on its body and wings. The adults fold their wings over their bodies when at rest or while feeding. The females deposit their eggs on the underside of leaves where they are usually clustered in groups. The number of eggs laid by females ranges from approximately 50 to 400, with an average of about 160. The eggs are very small, about 0.2 mm (1/125") long and 0.1 mm (1/250") in diameter. Each egg is attached by a stalk to the leaf and is somewhat elliptical in shape, tapering towards the unattached end. Newly laid eggs are smooth and whitish-yellow. As the eggs approach hatching in about 5 to 7 days, they turn brown. The pest goes through four nymphal instars, ranging in approximate size from 0.3 mm (1/95") as first instars and/or crawlers, to 0.6 mm (1/40") as fourth instars. The immature stages are thin and flat, elliptical in shape, and greenish-yellow in color. In most infestations, all stages of the life cycle are present. At the end of the nymphal cycle, it enters the pupal stage. The pupa has two conspicuous red eyes and the body is raised or convex in shape. It is yellow in color and about 0.7 mm (1/35") long. The nymphal stages are sedentary, with the exception of the crawler, which after hatching moves a very short distance. Once a feeding site is selected the nymphs do not move. They suck juices from the plant with their piercing-sucking mouthparts. The nymphs are located on the undersides of the leaves and can become so numerous that they almost cover the entire undersurface area. As the life cycle progresses from stage to stage, molting occurs and the cast skins (particularly from the pupae) remain on the leaves. These structures are empty, silver in color, and resemble small fish scales on the leaves. Adults congregate, feed, and mate on the undersurfaces of the leaves of the host plants. This can occur in such numbers as to create "clouds" when disturbed. They appear to be more active during the sunny daylight periods, and do not fly as readily during early morning, late evening, or night hours. The sweetpotato whitefly currently is known to attack over 500 species of plants representing 74 plant families. Feeding damage by both the nymphs and adults results in the accumulation of honeydew on the leaves, with subsequent growth of sooty black as well as other molds. The plants may have slow or abnormal growth. Other forms of damage include the removal of plant sap, vine, leaf, and plant breakdown, chlorotic spots, yellowing, leaf shedding and abnormalities of fruiting structure. Yields can be significantly reduced. It is believed that the pest injects foreign enzymes into the host plant while feeding, affecting the normal physiological processes. The pest also is known to vector virus diseases to a large number of crops.
Three-Cornered Alfalfa Hoppers. The three-cornered alfalfa hopper is related to the leafhopper. It is green in color, approximately 1/4 inch in length and stands about 1/4 inch high, being wedge-shaped and broad shouldered. It has rather prominent protruding eyes located low on its head. It pierces the tissues and sucks out plant juices. Its feeding causes the stem to scab over and exhibit a girdled appearance (which completely encircles the stem). The insect feeds deep in the plant foliage. The nymphs are similar in appearance to the adults but have spiny bodies and usually are more damaging than the adults.
Thrips. Thrips are about 1/16 of an inch long. The adults are dark and winged and the nymphs are wingless and yellow in color. They feed by rasping the young leaves of the bud and sucking out plant fluid. This results in scarred, deformed or "possum-eared" leaves. Thrips also are the vector of tomato spotted wilt virus (15). The timing of thrips infestations and damage are difficult to predict. Because the potential for thrips infestations cannot be predicted preplant and because thrips could be more easily and more reliably managed with at-planting insecticide treatments compared to curative treatments, significant acreage is treated annually for which monetary benefit is not immediately apparent. A significant factor in the widespread use of at-planting treatments for thrips management is the potential for thrips to interact with other stresses and reduce yields. Also, justifiable concerns exist about increased incidence of tomato spotted-wilt virus, a thrips vectored disease of peanut, has resulted in increased use of at-planting treatments for thrips management (3).
Velvetbean Caterpillars. Velvetbean caterpillars attack foliage, strip plants of leaves, and destroy the terminal buds. They tend to be most numerous late in the season just before to harvest. Velvetbean caterpillars are green to black in color and usually have stripes running the length of the body. The caterpillars can grow to 2 inches in length and are very active when disturbed. The adult moths are light brown and have a diagonal dark line across their wings from the front wing tip inward toward the body.
White Grubs. White grubs are the larvae of May or June beetles. They have a thick, white "C" shaped body with a brown head and three pairs of legs. They live in the soil and feed on underground plant parts. Grubs are most often a problem following sod crops.
Whitefringed Beetles. The whitefringed beetle is dark gray in color and about ˝ inch long and has a white fringe or band along the outer edges of the body. They feed on the outer margins of leaves. The larvae or grubs cause the principal damage by feeding on roots or other underground parts. The grubs are yellowish-white in color and are about ˝ inch long. They generally require 11 months for development into adults, but under some conditions may require up to 2 years or more. Whitefringed beetles normally overwinter as eggs or larvae. They usually produce one generation a year and spend all but about 3 months of their life in the soil (15,16).
Non-Chemical Insect Management
A long crop rotation program is essential for peanut production. The peanut plant responds to both the harmful and beneficial effects of other crops grown in the fields. A minimum of a 3-year rotation with a grass crop is recommended for reducing nematode and soilborne disease problems, whitefringed beetle damage, and permits better management of many weeds. Other non-chemical insect/mite management tactics include such things as modifying irrigation practices to manage pests, early planting, and late planting (3). Cotton is widely accepted in crop rotation with peanut, because each crop is resistant to the species of root-knot nematode that attacks the other.
Chemical Insect Management
According to the SilverPlatter SPIRS Pestbank Database, May 1999, there are a total of 26 different insecticidal active ingredients registered with EPA for insect management on peanut grown in Florida. Realistically, however, Florida peanut producers only use a fraction of these 26 active ingredients. Effective insect management depends on a combination of cultural and chemical practices. Insecticide products commonly used on peanut include phorate, chlorpyrifos, acephate, aldicarb, methomyl, lambda-cyhalothrin, carbaryl, and Bacillus thuringiensis (14). The use of systemic insecticides helps to eliminate the need for additional foliar insecticide sprays, unless pests such as worms or mites become a problem late in the season. Systemic insecticides are applied in furrow at the time of planting. Granular formulations are applied with a special row-type granular applicator. If possible, the insecticide granules, are placed slightly below the seed (16).
PHORATE (Thimet) - (median $/lb. a.i., $9.75) (90 day PHI); Phorate is an organophosphate insecticide commonly used to manage thrips and leafhoppers, but it also exhibits population reduction properties on other early season peanut pests such as corn rootworms if it is applied at pegging. It also tends to reduce the incidence of tomato spotted wilt virus. Phorate is applied to approximately 10 percent of the peanut acreage in Florida (19,23). A single application takes place predominately at planting but sometimes at pegging. When used at planting, the phorate granules are distributed evenly within the furrow of the row and buried along with the seed at planting at a rate of approximately 3.0 pounds of formulated product per acre. If applied at pegging, the granules are distributed as a band over the fruiting zone at a rate of approximately 3.0 pounds of formulated product per acre. If phorate is applied at planting, it should not be applied at pegging (14,15). The Thimet 20G label allows for a total of 15 pounds of formulated material to be applied per acre, but realistically, only approximately 3.0 pounds are applied (14). In the southeastern United States, phorate is applied at a total application cost of $1.8 million and provides a protection value of approximately $2.7 million, for a return ratio of 1.5:1 (3). Phorate has a restricted entry interval under the Worker Protection Standard (WPS) of 48 hours. If the product is soil incorporated, the WPS allows workers to enter the treated area when there will be no contact with anything that has been treated.
CHLORPYRIFOS (Lorsban 15G) - (median $/lb. a.i., $12.67) (21 day PHI); Chlorpyrifos is an organophosphate insecticide used to manage cutworms, lesser cornstalk borer and corn rootworm larvae, and to suppress wireworms. Chlorpyrifos is applied 1.0 time to approximately 35-45 percent of the peanut acreage in Florida (14,19,23). Chlorpyrifos applications aid in the suppression of white mold (Southern stem rot) (22), but has found little use for this purpose since the introduction of tebuconazole (Folicur) and azoxystrobin (Abound). A single application is suggested at planting or at pegging. When used at planting, chlorpyrifos granules are applied in a 6 to 12 inch band over the row behind the planter shoe and in front of the press wheel at approximately 10.0 pounds of formulated product per acre. If applied at pegging, the granules are distributed in a 6 to 18 inch band over the row, at approximately 12.0 pounds of formulated product per acre. If chlorpyrifos is applied at planting, it will not be applied at pegging, even though the repeat application is often recommended, because of economic considerations (14,15). The emulsifiable concentrate formulation is generally not used because it causes foliar burn (18). When used in the southeastern United States, chlorpyrifos provides $10.9 million in protection for a regional application cost of $6.15 million, giving a net return ratio of 1.8:1 (3). Chlorpyrifos has a restricted entry interval under the Worker Protection Standard (WPS) of 12 hours. If the product is soil incorporated, the WPS allows workers to enter the treated area when there will be no contact with anything that has been treated.
ACEPHATE (Orthene) - (median $/lb. a.i., $14.00) (14 day PHI); Acephate is an organophosphate registered for both seed treatment and foliar applications on peanut. As a seed treatment, acephate is primarily used for thrips management. Approximately 15 percent of the peanut seed planted in the state is treated, an average of 1.0 time. Acephate is applied evenly to seed at a rate of 4 ounces of formulated product (75S Soluble Powder, as allowed by Special Local Need Registration FL940002) per acre in the planter box as a dry powder. For treatment, the planter box is filled 1/3 full with seed, then 1/3 of the acephate is applied evenly over the surface of the seed. The planter box is then filled 2/3 full of seed, and another 1/3 of the acephate is evenly applied over the surface of the seed. Lastly, the planter box is completely filled with seed and the remaining 1/3 of the acephate is evenly distributed over the seed. Acephate cannot be mixed with the seed by stirring or other agitation, as such actions will result in unacceptable mechanical damage of the peanut seeds before planting. Also, air planters may not be used. When used as a foliar insecticide, liquid acephate is applied to approximately 10 percent of Florida’s peanut acreage, an average of 2.0 times (14,23) by either ground or air. It is used to aid in management of corn earworms, fall armyworms, grasshoppers, leafhoppers, loopers, thrips, and velvetbean caterpillars (14,15). Overall, when all acephate use is considered in the southeast United States, it is applied at a cost of $1.7 million and provides $6.1 million in protection value, for a return ratio of 3.6:1 (3). Acephate has a restricted entry interval under the Worker Protection Standard of 24 hours.
ALDICARB (Temik) - (median $/lb. a.i., $20.67) (90 day PHI); Aldicarb is a granular formulated carbamate insecticide used to manage thrips and nematodes. It is applied 1.0 time to approximately 20 to 55 percent of the peanut acreage in Florida (14,19,23). Typically, a single application takes place at planting for thrips management. When applied, the aldicarb granules are placed in the seed furrow at a rate of 7 to 10 pounds of formulated product per acre and immediately covered with soil. For nematode management, a Special Local Need 24(c) registration in Florida (FL780023) in place since 1978 allows aldicarb to be applied in split applications, once at planting and an additional application at peg initiation. Aldicarb is applied 2.0 times, at a rate of 10 pounds of formulated material per acre for each application. The seeds are then planted in the treated zone. When applied at peg initiation, the granules are applied in a band 12 to 18 inches wide over the row. The use of aldicarb is an expensive tactic in peanut grower’s pest management endeavor (14). In the Southeastern United States, aldicarb offers $16.3 million of protection annually, but does so at a cost of approximately $13.6 million. Therefore, the net returns ratio for aldicarb use is 1.2:1. Several alternative insecticides may provide more economical management of thrips. A foliar application of acephate, for example, provides efficacy at approximately one-half the cost. The apparent lack of return for aldicarb use is partially due to the fact that thrips management is often accomplished prophylactically because of the inability to predict which acres will be infested and what the potential damage is likely to be. Furthermore, it is a common opinion that thrips injury is often not damaging to peanut growth and yield, especially when environmental conditions are favorable, but when other early-season stresses occur simultaneously, thrips damage can reduce yield (3). Aldicarb has a restricted entry interval under the Worker Protection Standard (WPS) of 48 hours. If the product is soil incorporated, the WPS allows workers to enter the treated area when there will be no contact with anything that has been treated.
METHOMYL (Lannate) - (median $/lb. a.i., $23.33) (21 day PHI); Methomyl is a broad spectrum carbamate insecticide peanut growers use in their insect pest management programs. It is used to manage corn earworms, leafhoppers, fall and beet armyworms, green cloverworms, velvetbean caterpillars, cabbage and soybean loopers, cutworms, and grasshoppers. Methomyl is only applied during growing years that require treatment, as pests such as armyworms are not a problem every year. Methomyl and lambda-cyhalothrin are the only insecticides that provide acceptable beet armyworms management. When applications are necessary, methomyl is used on approximately 80 percent of the state’s peanut acreage at a rate of approximately 0.675 pounds a.i. per acre an average of 2.0 times. Methomyl is sometimes a preferential selection because it can be applied aerially. Growers report that its has a residual effectiveness of approximately 3 days in the field (14). When methomyl is used in the southeastern United States, it provides approximately 17 percent more protection value than its leading foliar-applied carbamate alternative, carbaryl, and has a return ratio of 5.7:1 (3). Methomyl has a restricted entry interval under the Worker Protection Standard of 48 hours.
LAMBDA-CYHALOTHRIN (Karate/Warrior) - (median $/lb. a.i., $325.70) (14 day PHI); Lambda-cyhalothrin is a synthetic pyrethroid insecticide, used primarily to manage armyworms, corn earworms, velvetbean caterpillar, leafhoppers, bean leaf beetles, vegetable weevils, alfalfa hoppers, stink bugs, thrips and grasshoppers, and to suppress populations of lesser cornstalk borers, mites and aphids (14-16). According to producers, lambda-cyhalothrin has 5 to 6 days of residual activity in the field (14). It is applied to approximately 50 percent of the state’s total peanut acreage at a rate of approximately 3.84 fluid ounces of formulated pruduct per acre an average of 1.0 time. It can be applied by either ground or air (14,15). Lambda-cyhalothrin has a restricted entry interval under the Worker Protection Standard of 24 hours.
CARBARYL (Sevin) - (median $/lb. a.i., $6.50) (14 day PHI for foliar sprays, 0 day PHI for granular applications); Carbaryl is a less-expensive insecticide occasionally used by peanut producers to manage insect pests such as thrips, leafhoppers, corn earworms, velvetbean caterpillars, alfalfa caterpillars, ants, bean leaf beetles, blister beetles, cucumber beetles, darkling groung beetles, field crickets, grasshoppers, green cloverworms, Mexican bean beetles, rednecked peanut worms, sowbugs, stinkbugs, alfalfa hoppers, webworms, and whitefringed beetles (14-16). Carbaryl is used on approximately 10 percent of the state’s peanut acreage at a rate of 0.8 to 2.0 pounds of a.i. per acre an average of 2.0 times (14,19,23). A major advantage of carbaryl is there is no limitation between days to harvest after application when using the granular formulation. It is sometimes a preferential selection because it can be applied aerially. When carbaryl is used in the southeastern United States, it provides return ratio of 4.9:1 (3). Carbaryl has a restricted entry interval under the Worker Protection Standard of 12 hours.
BACILLUS THURINGIENSIS- (median $/lb. a.i., $138.20) (0 day PHI, but Restricted Entry Interval of 4 hours); B.t. is occasionally used, in a prophylactic manner, by Florida peanut growers to manage Lepidopteran-type larvae pests. However, if worms are large in size, or if worm populations exceed threshold levels, then acephate, chlorpyrifos, methomyl, or carbaryl are used. B.t. is applied to less than 10 percent of the peanut acreage an average of 2 times (14,19). B.t. is not applied to peanut much because of cost and its short residual activity. It also does not provide as broad control of insects as other materials (19).
Peanut diseases reduce yields and monetary returns by retarding desirable plant development or by diverting product utilization. Some diseases, such as leaf spot and rust, are obvious in appearance while others, such as root rots and pod rots, often are unnoticed until dry weather occurs or until harvest. Other peanut diseases, such as yellow mold that is associated with aflatoxin, are evident in stored peanuts also. All peanut producers experience loss from one or more diseases that occur annually on their crop. Disease control strategies are an essential component of all peanut production programs. One or more diseases of peanut can always be found in fields from planting until harvest. Yield reductions associated with foliar diseases such as leaf spot pose the greatest threat of all diseases to southeastern United States. Early and late leaf spot can potentially cause annual losses in the range of $600 million. In some areas of Florida, tomato spotted wilt virus (TSWV) has caused a major peanut disease in recent years. Growers rely on resistant varieties, planting dates and plant populations, and a systemic insecticide applied at planting to reduce losses from TSWV. White mold and Rhizoctonia limb rot can cause damage. The magnitude of damage and resulting crop loss, however, varies with the time of occurrence, disease distribution, environmental conditions and, more importantly, the disease organism. Each of these factors will influence choices of control strategies needed. No one management measure will be totally effective in managing all peanut diseases, and a series of coordinated control measures is necessary to do a proper job. Each step requires knowledge and experience (22).
Seedling Blight. Seedling blight is caused by a variety of fungi including Rhizoctonia solani, Rhizopus sp., Lasiodiplodia theobromae, Diplodia sp., Aspergillus flavus, A. niger, and Pythium spp. Symptoms include pre-/or post-emergence death of the seedling accompanied by elongate sunken, brown, gray or black areas in young plant parts. The stem above the infected area is usually greater in diameter than the infected area. Roots become decayed. Seedlings are stunted and often die.
Root Rot. (Rhizoctonia spp., Pythium spp., Cylindrocladium parasiticum, Sclerotium rolfsii) Symptoms of root rot include sunken dark-brown areas in primary roots and a general browning of secondary roots. The lower stems develop dry, sunken, brown to black areas that later may girdle the entire stem near the soil line.
Crown Rot. (Aspergillus niger) Plants infected with the crown rot fungus are weak and may wilt; often many plants die. First signs of infection on seedlings are water-soaked tissues on the crown and roots. Fungicide sprays can be used to suppress crown rot.
Aerial Blight and Limb Rot. (Rhizoctonia solani) Leaves infected with this fungus have irregularly-shaped, lobed, tan leaf spots. As the spots expand in size, a greasy zone may be seen on the outer edge of the spots. Entire leaves and petioles may be infected. The vines (limbs) may have elongated tan spots up to 3 inches or more. Within these spots, growth bands may be visible. During periods with high humidity, a webbing of fungal growth (like spider webs or webs from spider mites) can be seen on and between leaflets and leaves.
Southern Stem Rot (Southern Blight, White Mold). (Sclerotium rolfsii) Stems, pegs, roots, pods and nuts are susceptible to infection with white mold. The first sign of infection is a sudden wilting of a stem branch. The leaflets may become yellow and turn reddish-brown; other branches wilt later. White mycelial growth may be found in lower parts of the stem and in nearby organic debris on the soil. Pegs may have lesions with shredding of the tissue. Later, hard, spherical structures called sclerotia occur. They are first white and soft, then light brown to pink, then dark brown and hard.
Peg and Pod Rots. Peg and pod rots are caused by a variety of fungi including Rhizoctonia solani, Pythium spp., Sclerotium rolfsii, Cylindrocladium parasiticum, and Cercosporidium personatum (pegs only). Symptoms on pegs include the development of light to dark brown lesions sunken or superficial, varying in size from small specks to entire peg blemish. Symptoms on pods appear as brown to black lesions on immature or mature pods. Spots may be angular, rough, or sunken. Extreme cases result in total decay and shredding. Adequate levels of calcium in the pegging zone will suppress pod rots. Appropriate management of soil insects and nematodes is necessary for management of peg and pod rots, as these organisms can predispose the plant to infection.
Diplodia Collar and Stem Rot. (Lasiodiplodia theobromae) This disease can appear similar to white mold, but the absence of mustard seed-sized sclerotia indicates the possibility of this disease. Collar rot is likely to appear within 50 to 60 days after planting but can occur later. Usually, the entire plant wilts whereas white mold causes wilting on a more gradual basis. Laboratory diagnosis is essential unless shredded necrotic stem has pin point-sized, black, pimple structures (pynidia) present. Black lesions can be present on the stems midway up the plant.
Leaf Scorch. (Leptosphaerulina crassiasca) Leaf scorch symptoms are usually found on tips of leaflets in a "v" shaped pattern. The first sign of this disease is yellowing and then death of the infected area. Necrotic areas surrounded by a yellow halo often with dark circular areas or concentric rings in the dead tissue can be seen. Stem lesions are black and may be over 6 inches long.
Peanut Rust. (Puccinia arachidis) The first symptoms of peanut rust appear as whitish-yellow green flecks on the leaflets. Within 48 hours, rust colored erumpent pustules occur (sori). Most pustules occur on the lower side of leaflets. Leaves yellow and then turn brown and finally fall off. Infected areas in the field are often first noticed because of yellowing plants in a limited area. Later, plants in these areas die and rust pustules are evident on petioles, stems, and pegs (20). Rust can be redistributed over the entire field if left unchecked, and infection causes the plants to be harvested early, which reduces yield (14). Crop rotation, destruction of volunteer peanuts, and fungicide sprays will reduce the impact of this disease.
Yellow Mold. (Aspergillus flavus, a source of aflatoxin) Currently, diagnosis of this disease is made at the buying point. Inspectors look for signs of the fungus from random samples. This disease is more common in dry seasons and on damaged peanut. For more details, refer to the earlier discussion on aflatoxin.
Peanut Mottle. Peanut mottle is a seedborne viral disease that can be spread by aphids. Symptoms include a leaf mottle (diffuse shades of greens and yellows) that occurs on the leaflets. Laboratory diagnosis is necessary to confirm this disease.
Peanut Stripe. Peanut stripe virus is spread by aphids and by seed. Symptoms include discontinual, dark green striping along the lateral veins on newly infected leaves. With time, an oak leaf dark-green pattern or green blotch occurs on leaflets. Stunting of plants has not been associated with this virus, and the virus is not known to cause a reduction in yield in Florida.
Tomato Spotted Wilt. Tomato spotted wilt virus causes a serious disease of peanuts in Florida and was first discovered in peanut in the state in 1986. Tomato spotted wilt virus is a thrips-vectored virus, causing white etching-like ringspots on leaflets. Stunting of plants occurs if the infection occurs early. Buds may die and turn brown, and plants may be abnormally yellow (20).
Peanut Leaf Spot. Each year, peanut producers in Florida contend with a foliar disease complex commonly referred to as peanut leaf spot. The fungus Cercospora arachidicola causes early leaf spot, and the fungus Cercosporidium personatum causes late leaf spot. Sometimes early leaf spot predominates during May, June, July and August, while late leaf spot predominates during the remainder of the season. Late leaf spot can predominate throughout the season. Leaflets, petioles, stems and pegs are infected. Symptoms include brown-black spots with or without rough margins, sometimes having a halo around the spot. Some chemical burns are similar in appearance to early leaf spot. Peanut leaf spot causes premature defoliation of the peanut plants. Premature defoliation weakens the plant and so the plants must be harvested prematurely, which results in reduced yield. Yield losses may vary from near zero to as much as 91 percent (in research tests). On a statewide basis in Florida, annual yield losses attributed to peanut leaf spot vary from 5 to 40 percent (20,21).
Non-Chemical Disease Management
Nonchemical tactics for foliar disease management are important, but when used alone they will not permit sustained peanut production in Florida. Relying exclusively on nonchemical tactics compromises regional production and value by approximately 24 percent (3).
Crop Rotation. Whenever possible, an interval of 3 to 4 years between peanut crops on the same land is preferable. Shorter intervals increase the occurrence of most peanut diseases. A soybean-peanut rotation may not be an appropriate rotation, because soybean is highly susceptible to the white mold fungus (Sclerotium rolfsii). Considering all peanut diseases, it is best to rotate with grass crops (pastures), or sorghum, since many fungi causing diseases of grass crops do not cause diseases of peanut and vise versa. Also, studies show that fungi that produce aflatoxin will be in higher populations with rotations including corn and peanut.
Site Location. If possible, it is not advisable to locate a peanut field next to a field that had peanut the previous year. Peanut leaf spot has been more severe along the edges of fields next to an old planting site. Fields of tomato and peanut should be spaced as far from each other as possible to reduce the spread of tomato spotted wilt virus by thrips from crop to crop.
Deep Plowing and Land Preparation. When the soil is turned during land preparation, every effort is made to bury surface trash and stubble at least 6 inches deep, even if a grass crop precedes the peanut crop. This tactic is specifically aimed at reducing white mold and other soilborne diseases. It also is beneficial in reducing leaf spot when the interval between peanut crops is only 1 or 2 years. Planting peanut in a no-till situation can have both good and bad results. Seedlings and young plants are highly susceptible to soilborne fungi. Poor stands can result when the producer uses a single disk opener for the seed furrow. Better stands result when a subsoiler with a single disk opener is used or if a rolling basket cultivator is used. The shank of the subsoiler or rolling basket clears away organic matter from the emergence zone, which suggests that pushing away some of the organic trash from the immediate planting zone can be beneficial (22). The practice of strip-till is just now beginning and will probably become more popular because of soil and cost savings.
Lime and Fertilizer Relations with Peanut. Peanut is a high calcium-requiring crop. Calcium availability and placement are critical for improved quality and yields. Deficiency of calcium in the fruit predisposes the plant to peg and pod rots caused by fungi. Calcium deficiencies usually result from inadequate calcium in the pegging zone or competition from excess cations such as potassium, magnesium, or ammonium.
Weed Management. Less limb rot and other soilborne diseases occur where herbicides are used rather than cultivation (improper) for weed management. Cultivation frequently increases damage to plants and often results in soil and debris being deposited on the peanut plant. These conditions are ideal for development of white mold and other soilborne diseases. Caution should be used with herbicides since intensive use of certain ones will stress peanut plants. Cultivation with sweeps oriented in a flat position in row middles before root growth in that zone is not expected to increase disease. Leaf spot and rust are more difficult to manage where weeds are present. Weeds interfere with spray deposition and allow leaf wetness periods to be extended. Spores from the fungal diseases produced near the weeds serve as an intense inoculum source, thereby offsetting desired control.
Nematode Management. Nematodes cause wounds in peanut roots, pegs, and pods that create an entry site for fungi. Pod rot and white mold can be suppressed by reducing damage from nematodes.
Use of Quality Seed. Purchasing high germinating seed with good vigor reduces peanut diseases. Using high quality seed reduces seedling diseases caused by fungi. Also, a denser stand of peanut is likely to have a lower incidence of tomato spotted wilt.
Resistant Varieties. Some peanut varieties have intermediate resistance to diseases. Where resistance to leaf spot exists, fewer applications of fungicides may be required. Marketability of resistant varieties remain a concern for certain shellers and processors, because they should be kept separate from other varieties for efficient shelling. Resistant varieties are currently available to leaf spot, rust, white mold, tomato spotted wilt, and Cylindrocladium black rot.
Adjusting Planting Dates. Earlier planting reduces the impact of peanut leaf spot. Peanut planted in early- to mid-April in Florida may not have to be sprayed with fungicides until they are 60 days old, compared to 25 to 35 days after planting for peanut planted during May to early June. Tomato spotted wilt virus is spread by thrips, and populations of thrips are somewhat lower during May. Therefore, planting early to reduce leaf spot may result in more tomato spotted wilt than if planting is done in May. Also, planting too early into cool soils may result in more seedling blight. Higher seeding rates need to be used for planting in April, to compensate for plants lost to seedling blight. Later plantings have resulted in higher levels of aflatoxin in association with more lesser corn stalk borers. Later plantings are likely to have less damage from Cylindrocladium black rot.
Avoiding Deep Planting. Planting excessively deep will offset benefits from seed treatment fungicides. The longer it takes for a seedling to emerge, thus the longer the entire plant is exposed to soilborne fungi. Recommended planting depths are 2 to 3 inches in light textureed soils and 1.5 to 2 inches in heavy textured soils.
Minimizing Stress on the Roots. Excessive use of herbicides, excessive wetting and drying of soils, and nematode infection can weaken the root system and reduce the rate of growth, thereby allowing "weak" fungi to colonize root tissue and reduce plant vigor (22).
Chemical Disease Management
Effective disease management depends on the use of a combination of cultural and chemical practices. Fungicides used as preplant seed treatments include captan and thiram. Foliar fungicide products commonly used on Florida peanut include the coppers, sulfur, benomyl, tebuconazole, propiconazole, chlorothalonil, mancozeb, and azoxystrobin (14). When using boom-type ground application equipment, hollow cone or flat-fan nozzles are used. Three nozzles per row are used with one nozzle over the center and the other two on the sides of the row coupled with swivels that are reaimed with each successive spray application. For disease management, spray volumes from 15 to 250 gallons per acre perform well, and volumes of 15 to 50 are commonly used in commercial production. Spray pressures in the range of 40 to 400 psi are used. Injections of fungicides through irrigation units are not likely to perform as well as boom-type sprayers unless a low volume, low pressure irrigation system is used (22).
CHLOROTHALONIL (Bravo/Terranil) - (median $/lb. a.i., $8.33) (14 day PHI); Chlorothalonil is the fungicide peanut producers use the most in their chemical disease management activities. This material is a polychlorinated aromatic fungicide, used to manage leaf spot, rust, web blotch, and aerial blight and limb rots. Nearly all acreage in Florida is treated annually at an average rate of approximately 1.1 pounds of active ingredient per acre. The number of applications per season can range from 4 to 8, depending on the environmental conditions affecting the crop (20,22,23). In the southeast United States, chlorothalonil itself is applied at a total application cost of $40 million and provides a protection value of approximately $212 million, for a return ratio of 5.3:1. The short-term value of lost production would likely exceed $155 million annually in the southeast United States (3). Peanut is the predominant recipient crop of chlorothalonil, with approximately 34 percent of the total chlorothalonil used in the United States being applied to peanut. The next highest use of chlorothalonil is on potato, which accounts for 12 percent of the total chlorothalonil used in the United States. Use of chlorothalonil on all labeled crops represents approximately 15 percent of all Untied States fungicide use by weight (25). Chlorothalonil has a restricted entry interval under the Worker Protection Standard of 48 hours.
TEBUCONAZOLE (Folicur) - (median $/lb. a.i., $121.09) (14 day PHI); Folicur is a sterol-inhibiting systemic fungicide used to manage leaf spot, rust, white mold, and Cylndrocladium black rot. It is applied an average of 4.0 times, at a rate of approximately 0.2 pounds of active ingredient per acre. Tebuconazole has a restricted entry interval under the Worker Protection Standard of 12 hours. Aerial application of tebuconazole is prohibited.
PROPICONAZOLE (Tilt) - (median $/lb. a.i., $95.83) (14 day PHI); Propiconazole also is a sterol-inhibiting fungicide, used primarily to manage early leaf spot. It is applied at a rate of approximately 0.125 pounds of active ingredient per acre. Propiconazole has a restricted entry interval under the Worker Protection Standard of 24 hours.
FLUTOLANIL (Moncut) - (median $/lb. a.i., $47.66) (40 day PHI); Flutolanil is a fairly new fungicide that is systemic in action used to manage white mold and limb rot. It is applied an average of 1 to 2 times, at a rate that does not exceed 2.0 pounds of active ingredient per acre per season. Flutolanil has a restricted entry interval under the Worker Protection Standard of 12 hours.
BENOMYL (Benlate) - (median $/lb. a.i., $35.00) (14 day PHI); Benomyl is a systemic-acting benzimidazole fungicide used primarily to aid in management of crown rot. It is applied an average of 2.0 times, at a rate of approximately one-eighth of a pound of active ingredient per acre. It is not recommended to apply benomyl as a stand-alone fungicide; that is, it must be applied in combination with a labeled non-benzimidazole fungicide. Benomyl has a restricted entry interval under the Worker Protection Standard of 24 hours.
MANCOZEB (Manzate/Dithane/Penncozeb/ Manex II) - (median $/lb. a.i., $3.88) (14 day PHI); Mancozeb is a contact-action fungicide in the EBDC chemical family, used primarily to aid in management of leaf spot and rust. It is applied at a rate of approximately 1.2 pounds of active ingredient per acre. It is recommended that mancozeb applications start when rust diseases are reported in the area. Mancozeb has a restricted entry interval under the Worker Protection Standard of 24 hours.
SULFUR - (median $/lb. a.i., $1.00); Sulfur is a fungicide that when used, is used in combination with other fungicides such as chlorothalonil. It is used primarily to aid in management of leaf spot and rust. Sulfur is not regarded as an adequate stand-alone treatment of peanut diseases. It is applied to approximately 30 percent of Florida’s peanut acreage (23) an average of 4.0 times, at a rate of approximately 3.0 to 4.5 pounds of active ingredient per acre (14). Sulfur has a restricted entry interval under the Worker Protection Standard of 24 hours. The use of sulfur also provides some nutritional value for the peanut plant.
COPPER (many brands) - (1or 2 day PHI); Copper fungicides, like sulfur, are commonly used in combination with other fungicides on peanut. It is used primarily to aid in management of leaf spot. Copper, like sulfur, is generally not regarded as an adequate stand-alone treatment of disease. It is applied at a rate of approximately 1.2 to 2.3 pounds of active ingredient per acre. When applied, it is typically applied late in the growing season. Copper has a restricted entry interval under the Worker Protection Standard of 48 hours. The use of copper also provides some nutritional value for the peanut plant.
AZOXYSTROBIN (Abound); Azoxystrobin is a fairly new fungicide used to manage white mold, leaf spot, lime rot, and rust. It is applied to approximately 20 percent of Florida’s peanut acreage an average of 1 to 2 times, at a rate that does not exceed 0.8 pounds of active ingredient per acre per season. Azoxystrobin has a restricted entry interval under the Worker Protection Standard of 12 hours.
Successful weed management in peanut involves using good management practices in all phases of peanut production. Weeds compete with peanut plants for moisture, nutrients, and light, with the greatest competition usually occurring during the first 6 weeks after planting. Although late-season weeds may not be as competitive as early-season weeds, they interfere with harvesting operations and also with fungicide and insecticide applications (24). Additionally, many weed species serve as alternate hosts for certain peanut pests such as armyworms, loopers and aphids, as well as plant pathogens and nematodes. Since weeds also can provide shelter and food for natural enemies of peanut insect pests, weed management strategies should adequately address the positive and negative role of weeds in and around the peanut field. The most important weed pests in Florida peanut production are yellow and purple nutsedge, bristly starbur, Florida beggarweed, Florida pusley, morningglory, pigweed, sicklepod, wild poinsettia, hairy indigo, crabgrass, goosegrass, johnsongrass, and Texas panicum (24,28).
NUTSEDGE (Cyperus spp.). Yellow nutsedge (C. esculentus) and purple nutsedge (C. rotundus) constitute the greatest weed problem in Florida peanut. Both of these perennial sedges are found in disturbed habitats throughout Florida and the southeast United States. Yellow nutsedge may produce some seed but reproduces primarily by rhizomes and tubers. The first plant develops rhizomes, which end in bulbs or tubers that produce new plants. Tuber production is favored by low nitrogen levels and high temperatures (80 to 91 F). This weed is tolerant of high soil moisture but is intolerant of shade. Purple nutsedge also is able to reproduce from tubers when conditions are harsh, making it difficult to control. Unlike the rhizomes of yellow nutsedge, purple nutsedge rhizomes growing off the first plant produce new plants in a series ("tuber-chains"). The plant also reproduces by seed to a limited degree. Although purple nutsedge also is intolerant of shade, it is able to survive a wide range of environmental conditions, growing well in nearly all soil types and over a range of soil moisture and soil pH. It also is able to survive extremely high temperatures.
PIGWEED (Amaranthus species). Several species of pigweed are common weeds in Florida, including smooth pigweed (A. hybridus), spiny amaranth (A. spinosus) and livid amaranth (A. lividus). Pigweeds are summer annuals with taproots. These broadleaf plants reproduce by seed and can reach heights of six feet. Researchers have found short pigweed seedlings to be susceptible to mole cricket damage, and pigweeds may therefore serve as alternative food sources on which mole cricket populations develop before moving into other crops.
GRASSES. Grasses, such as crabgrass (Digitaria spp.), goosegrass (Eleusine indica), Texas panicum (Panicum texanum), and johnsongrass (Sorghum halepense) also can be a problem for peanut growers in Florida. Crabgrass, a summer annual, roots at the nodes and reproduces by seed. It flowers from June to October. Goosegrass, also a summer annual that flowers from July to October, is similar in appearance to crabgrass but grows in tufts and does not root at the nodes.
BRISLY STARBUR (Acanthospemum hispidum). Bristly Starbur is an upright annual with dichotomous (Y-shaped) branching. The Y-shaped form of branching gives the plant one of its common names, Slingshot Weed. The stems are densely covered with hairs. These hairs can be stiff and bristly or soft and flexible. The leaves have no stalk (sessile) and are opposite each other on the stem. They are oval to triangular-ovate in shape with a base that narrows rapidly to the stem. Some leaves can be up to 11.5 cm long. The margins of the leaves can have irregular teeth or they may be entire and smooth. Like the stems, the leaves are hairy, with hairs are on both the upper and lower surfaces and on the margins. The lower leaf surface also is dotted with glands. The flowers are similar of those of the aster or daisy family. Each head has 5 to 9 ray flowers. The petals (corollas) of the ray flowers are pale yellow and are about 1.5 mm long. The disc flowers in the center of the head are sterile. The fruits are flattened and triangular in shape. These fruits are covered with stiff, hooked hairs and have either a straight or curved pair of spines at the top. The bristly appearance and grouping of several fruits in each head provides the most frequently used common name, Bristly Starbur. Each fruit, excluding the terminal spines, is 5 to 6 mm long. The terminal spines are strongly divergent and are about 4 mm long. These terminal spines supply yet an additional common name, Goathead.
FLORIDA PUSLEY (Richardia scabra). This weed is an erect to prostrate, loosely branched annual. The stems are hairy, up to 80 cm long and do not usually root at the nodes. The leaves are oppositely arranged, ovate to elliptic-lanceolate shaped, up to 6.5 cm long and 2.5 cm wide. The leaves may be almost smooth, except for the margins, to rough on both leaf surfaces, and predominantly rough on principle veins. The leaf apex may be rounded to pointed. The leaf base is tapered with petioles ranging from very short to about 5 mm long. The opposite leaves are connected by a sheath with several ascending, hair-like appendages from 2 to 5 mm in length. The flowers are in a terminal head-like cluster composed of 20 or more flowers. The head is usually subtended by two pairs of leaves. The second or upper pair is usually much smaller than, and at right angles to, the lower pair of leaves. The outer part of the flower consists of six narrow lobes. These lobes are joined at the base forming a tube. The petals also are united and are usually white to occasionally pink or lavender and funnelform in shape. The tube ranges in length from 2 to 8 mm and the lobes of the petals are from 0.5 to 2.5 mm long. Each flower typically produces three nutlets from 2 to 3.5 mm in length and about 1.5 to 2 mm in width. The nutlets are more or less oblong to obovate shaped. The outer surface of the nutlet is covered with wart-like protuberances.
MORNINGGLORY (Ipomoea spp.). There are several morningglory weeds that affect peanut production. The sharp-pod morningglory, for example, is a sparsely hairy perennial that flowers the first year. The leaves are heart shaped with a sharp tip. The leaf margin may be smooth, 3-lobed or occasionally 5-lobed. The leaf size is usually less than 9 cm long and 7 cm wide, although some specimens may be up to 10.5 cm long and 8.8 cm wide. The flower stalks commonly bear from 1 to 5 flowers (rarely up to 10) on the non-hairy stalks. The stalks are rough textured due to the presence of short, broad growths or protuberances. The sepals (outer layer of the flower) are somewhat leathery, oblong-elliptic in shape and have a sharp tip. They may be as long as 15 mm and range from smooth to hairy at the base, but usually have fine hairs along the margins. The joined petals range from pink to purple (rarely white) in color, and are up to 4.5 cm long and about as broad. The stigma and stamens are shorter than the flower tube. The fruit is a hairy, spherical capsule up to 9 mm broad.
SICKLEPOD Sicklepod is an annual with erect, nearly hairless stems. The leaves are compound with 3 to 10 leaflets and a conspicuous gland about 2 mm long between, or just above, the lowest pair of leaflets. The terminal pair of leaflets is frequently larger than the lower pairs of leaflets. The leaflet blades are broader toward the tip and smooth above and below. The leaflet margins have short, appressed hairs. The leaflet base is asymmetrical and the leaflet tip is usually rounded with a tiny sharp point. The leaflets also are photosensitive. (The leaflets fold upward by flexible petioles at night or on cloudy days.) The stipules are hairy, linear and about 1 to 2 cm long. The flowers are axillary and usually solitary with yellow petals 8 to 17 mm long. The petals are unequal in shape and size. The sepals are unequal, 5 to 10 mm long and 2 to 5 mm wide. The fruit is a slender pod up to 18 cm long, 5 mm wide, 4-angled in cross section and usually curved downward. The pods are green and turn brown as the seeds mature. The seeds are 4 to 6 mm long, angular, light to dark brown in color, with two scars on the opposite surfaces oriented along the longest axis of the seed.
Non-chemical Weed Management
Crop Rotation. Crop rotations are an important part of the peanut weed control program. Certain broadleaf weeds, which are not easily controlled in peanut, may be controlled by herbicides that can be used in a preceding crop such as corn.
Cultivation. Cultivation can be used if effective weed control is not achieved with herbicides. However, if weeds have been controlled with herbicides, there is generally little benefit from cultivation. If cultivation is needed, throwing soil on the peanut vines must be avoided. Soil thrown on the vines may result in increased incidence of stem rot (white mold) and limb rot (28).
Chemical Weed Management
Herbicides are the most effective method for controlling weeds in peanut. Before purchasing a herbicide, you should first know your weed problem, since many herbicides are most effective on certain weeds. The most effective weed control and highest peanut yields have generally been obtained using a herbicide program consisting of a preplant incorporated treatment, followed by a cracking stage treatment, followed by a postemergence treatment. Maximum effectiveness will be achieved if application is timed to the emergence of the weeds. It needs to be noted that peanut under stress from cold weather, thrip injury, etc., may be subject to more injury from improper applications (24). It is also critical to plan on what crops will be planted following peanut. Some crops have more than one planting season set backs.
PENDIMETHALIN (Prowl) - (median $/lb. a.i., $7.50) (45 day PHI); Pendimethalin is a dinitroanaline herbicide that is applied preplant incorporated in peanut. It is used primarily for the management of weeds such as Florida pusley, pigweed, hairy indigo, crabgrass, goosegrass, johnsongrass, and Texas panicum. It is applied to approximately 50 percent of Florida’s peanut acreage an average of 1.0 time, at a rate of approximately 0.8 pounds of active ingredient per acre per season (14,23). Pendimethalin has a restricted entry interval under the Worker Protection Standard of 24 hours. Pendimethalin can be applied up to 60 days before planting. It must be incorporated within 7 days of application.
ETHALFLURALIN (Sonalan) - (median $/lb. a.i., $10.50); Ethalfluralin also is applied preplant incorporated in peanut. It is used primarily for the management of weeds such as Florida pusley, pigweed, hairy indigo, crabgrass, goosegrass, johnsongrass, and Texas panicum. It is applied to approximately 50 percent of Florida’s peanut acreage an average of 1.0 time, at a rate of approximately 0.56 pounds of active ingredient per acre per season (14,23). Ethalfluralin is mechanically incorporated into the soil as soon as possible after application and, to prevent loss of herbicidal activity, incorporation is not delayed more than 48 hours after application. Ethalfluralin has a restricted entry interval under the Worker Protection Standard of 24 hours.
IMAZAPIC (Cadre) - (median $/lb. a.i., $30.00); Imazapic is a post-emergence weed management herbicide used in peanut production. It is used primarily in the management of nutsedge, but it also suppresses weeds such as brisly starbur, cocklebur, Florida pusley, morningglory, pigweed, sicklepod, hairy indigo, crabgrass, goosegrass, johnsongrass, and Texas panicum. It is applied to approximately 75 percent of Florida’s peanut acreage an average of 1.0 time, at a rate of approximately 0.063 pounds of active ingredient per acre per season (14). Imazameth has a restricted entry interval under the Worker Protection Standard of 12 hours.
CHLORIMURON ETHYL (Classic) - (median $/lb. a.i., $44.00) (45 day PHI); Chlorimuron ethyl is a post-emergent herbicide typically used in peanut to manage larger weeds (up to 10 inches) late in the season. It is used primarily in the management of weeds such as Florida beggarweed, but it also is used in the suppression of hairy indigo, Florida pusley, morningglory, pigweed and sicklepod. It is applied to approximately 40 percent of Florida’s peanut acreage an average of 1.0 time, at a rate of approximately 0.001 pounds of active ingredient per acre per season, making it a relatively inexpensive late season weed management herbicide (14,23). Chlorimuron ethyl has a restricted entry interval under the Worker Protection Standard of 12 hours. Chlorimuron ethyl cannot be applied until 60 days after the youngest peanut plants have emerged.
METOLACHLOR (Dual II Magnum) - (median $/lb. a.i., $13.22) (90 day PHI); Metolachlor is a herbicide used at the cracking stage (that time when the soil cracks due to the emerging peanut seedling) primarily for pigweed, crabgrass, goosegrass, Florida beggarweed, and Florida pusley management. It is applied to approximately 35 percent of Florida’s peanut acreage an average of 1.0 time, at a rate of approximately 3.0 pounds of active ingredient per acre per season (14,23). Metolachlor has a restricted entry interval under the Worker Protection Standard of 24 hours.
IMAZETHAPYR (Pursuit) - (median $/lb. a.i., $343.04) (85 day PHI); Imazethapyr is a herbicide used at the cracking stage primarily for nutsedge, wild poinsettia, pigweed, morningglory, cocklebur and bristly starbur management. Imazethapyr is one of the most effective herbicides for management of wild poinsettia (3). It is applied to approximately 15 percent of Florida’s peanut acreage an average of 1.0 time, at a rate of approximately 0.06 pounds of active ingredient per acre per season (14,23). Imazethapyr has a restricted entry interval under the Worker Protection Standard of 4 hours.
2,4-dichlorophenoxy butyric acid (2,4-DB) - (median $/lb. a.i., $12.57) (90 day PHI); 2,4-DB is a postemergent herbicide used primarily for broadleaf weed management. 2-4-DB is one of the better treatments for the management of sicklepod (3). It is applied to 90 percent of Florida’s peanut acreage an average of 1.0 time, at a rate of approximately 0.4 pounds of active ingredient per acre per season (14,23). It is the most widely used peanut herbicide in the Southeastern United States. The net returns to treatment estimated for Southeastern United States acreage where 2,4-DB is applied exceeds $261 million. The next best economic alternative has a net returns to treatment estimate of less than $188 million for the same acreage (3). 2,4-DB has a restricted entry interval under the Worker Protection Standard of 48 hours.
PARAQUAT (Starfire) - (median $/lb. a.i., $13.80); Paraquat is a post emergent non-selective herbicide. It is generally used at the cracking stage for non-selective control. Paraquat is applied to 100 percent of Florida’s peanut acreage an average of 1.0 time, at a rate of approximately 0.9 pounds of active ingredient per acre per season (14,23). Paraquat has a restricted entry interval under the Worker Protection Standard of 48 hours.
BENTAZON (Basagran) - (median $/lb. a.i., $17.50) (30 day PHI); Bentazon is an "at cracking" applied herbicide used primarily for management of weeds such as bristly starbur, cocklebur, pigweed and morningglory. Bentazon, included as a tank mix with paraquat, will reduce damage to the peanut plant from the cracking time herbicide application. It is applied to approximately 90 percent of Florida’s peanut acreage an average of 1.0 time, at a rate of approximately 1.0 pound of active ingredient per acre per season (14,23). Bentazon has a restricted entry interval under the Worker Protection Standard of 12 hours.
SETHOXYDIM (Poast/Poast Plus) - (median $/lb. ai., $50.00) (40 day PHI) Sethoxydim is a postemergent herbicide used primarily for crabgrass, goosegrass, johnsongrass and Texas panicum management. It is applied to approximately 20 percent of Florida’s peanut acreage an average of 1.0 time, at a rate of approximately 0.47 pounds of active ingredient per acre per season (14,23). Sethoxydim has a restricted entry interval under the Worker Protection Standard of 12 hours.
ACIFLUORFEN (Blazer) - (median $/lb. ai., $32.00) (75 day PHI) Acifluorfen is an at-cracking/post emergent herbicide used primarily for management of Florida pusley, hairy indigo, Florida beggarweed, cocklebur and pigweed. It is applied to approximately 15 percent of Florida’s peanut acreage an average of 1.0 time, at a rate of approximately 0.375 pounds of active ingredient per acre per season (14,23). Acifluorfen has a restricted entry interval under the Worker Protection Standard of 48 hours.
The plant-parasitic nematodes that affect peanut are microscopic roundworms usually found in soil. General symptoms of nematode damage include stunting, premature wilting, leaf yellowing and related symptoms characteristic of nutrient deficiencies. Stunting and poor stand development tend to occur in patches throughout the field as a result of the irregular distribution of nematodes within the soil. Nematodes are not pests, per se. Not in the sense that we use them with insects, rodents, and weeds, which are non-pathogenic, non-disease causing organisms. Nematodes are disease causing pathogens (i.e., root-knot is the disease, root-knot nematode is the pathogen).
Peanut Root-Knot Nematode. The peanut root-knot nematode (Meloidogyne arenaria race 1) is the most serious nematode pathogen of peanut in Florida. It attacks peanut roots, pegs and pods throughout the season, stunting plants and reducing yields; direct injury to pods reduces quality. Increased pod rot often is associated with root-knot nematode galls. Infections of peanut by root-knot nematode can increase the severity of white mold and other soilborne diseases. Controlling this nematode in sandy soils often increases yields by more than 1,000 pounds per acre. Juvenile root-knot nematodes are found throughout the year, and along with eggs constitute the major survival stage. Juveniles infect plants soon after planting. Soon after blooming and initiation of pod set (35 to 45 days post planting), root-knot nematode juveniles may infect pegs and pods. Early infection may result in a weakened peg so that pods are lost in the soil or fall off during harvesting. Shells of pods that set may become heavily infected and extensively galled late in the season, which may result in heavy yield losses. Root-knot nematodes are capable of producing many generations on a long season crop such as peanut, thus making it one of the most challenging crops for practicing nematode management techniques.
Lesion Nematode. All life stages of the lesion nematode (Pratylenchus brachyurus) except the egg and males are infective. The nematode may penetrate anywhere on roots, pegs or pods. Lesion nematodes can suppress yield by several hundred pounds per acre by injuring pegs so severely that pods break off from the plants when they are turned up at harvest. The lesions these nematodes cause also can increase pod rot.
Ring Nematode. Ring nematodes (Mesocriconema spp.) are sometimes associated with reduced peanut yields. This nematode feeds on the outside of roots by thrusting its long stylet into the root tissue.
Nematode Monitoring and Field Choice. Peanut is one of the most profitable agronomic crops in Florida, so it should be planted only in fields with the best yield potential. Fields with unusually high risks of nematode or other pest and disease problems should be avoided. To determine the suitability of each field for planting peanut, the producer should know which nematodes are present and their severity. Nematode infestations should be mapped based on symptoms seen on susceptible crops and laboratory assay of samples. Both are needed to have best information about all kinds of nematodes present and their distribution.
Field Mapping. The best information about distribution of nematode densities comes from records from previous seasons: a field map based on direct observations from many locations in the field provides far better information about nematode distribution than one can obtain from soil samples. Root-knot nematode symptoms are relatively easily monitored by observing galling of peanut roots and pods. Root-knot nematodes cause galls on many plants that make it easy to map their incidence in the field. However, there are several types of root-knot nematodes that infect many plant species, but not necessarily peanut. To be sure that a population can damage peanut, galls must be seen on peanut. Identification of the peanut root-knot nematode species is relatively easy in the laboratory, but host race 1, which infects peanut, is not separated easily from host race 2 (does not infect peanut); they look identical under the microscope. Race separation depends on their ability to infect peanut plants. Lesion nematodes cause dry, brown lesions on roots, pegs and pods of peanut, therefore this nematode also can be monitored based on these symptoms. Pod lesions caused by pathogenic fungi usually are larger and not as discrete as those caused by lesion nematodes.
Nematoded Advisory. Identifying all kinds of nematodes associated with a problem or in a field for which plans are being made and their relative numbers depends on extraction of nematodes from soil and root samples by a nematology laboratory. Samples of soil and roots are best taken in the autumn or early winter, shortly before or after harvest of crops. Samples taken later, up to 1 month before planting, can help identify the kinds of nematodes present, but are less useful for detecting low numbers of nematodes or predicting damage.
Economic Damage Threshold Determination. University experiments have been conducted to determine the relationship between yield of peanut and preplant peanut root-knot nematode densities. In three tests, 1 to 5 nematodes per ˝ pint of soil resulted in 10 percent pod losses, and thresholds for plant damage were 1 nematode per ˝ pint of soil. The latter is at the limit of detection. Since the tolerance limit of peanut to the peanut root-knot nematode in most seasons is quite close to the limits of detection, it is critical to sample whenever chances of detection are greatest. The final population density (nematode numbers) at or near harvest of the previous crop provides the best opportunity to detect peanut nematodes.
Crop Rotation. Peanut should follow crops that are poor hosts of peanut root-knot nematode, such as small grains (avoid wheat because some cultivars are very good host for the peanut root-knot nematode) or pasture grasses. Peanut following crops such as tobacco or vegetables should be avoided because these crops are good hosts for the peanut root-knot nematode. Field corn is only fair for reducing root-knot nematode populations but is better than continuous peanut or other good hosts of the nematode. Some cultivars are very good hosts for the peanut root-knot nematode, whereas others are poor hosts. Grain sorghum appears to suppress root-knot nematode population densities 2 to 4 times better than corn. Cotton fits well in rotation with peanut, since the peanut root-knot nematode does not live on cotton, and the root-knot nematode that infects cotton does not live on peanut. Several years of bahiagrass have long been recognized as one of the best rotations to precede peanut. However, control of weeds in a bahiagrass planting is essential. Hairy indigo, alyceclover, and morningglory are a few common weeds that are good hosts for peanut root-knot nematode. Long rotations of 3 or more years out of peanut and other favorable hosts are better than 1- or 2-year rotations. Rotation should not be expected to reduce a root-knot nematode population abruptly because:
- Some of a nematode population will survive the winter without a host;
- Most crop plants can support at least a little nematode reproduction; and,
- Most fields have some weeds that support nematode reproduction.
Crop rotation is a far better tool to help keep relatively low population densities from getting too high, or to gradually reduce high populations over several years. Unfortunately, rotations are of little value for reducing lesion nematode numbers, because the nematode lives well on so many different crops, including most grass family crops, soybean, and most vegetables.
Fallowing. Fallow (leaving a field unplanted to reduce pathogens and pests through lack of host plants on which to live) is often tried as an alternative to planting and maintaining an unprofitable rotation crop. Theoretically, it should reduce nematodes and other pathogens or pests that must feed on living plants. However, fallowing has several limitations as a nematode management practice. First, it is rare that a "fallow" field is truly lacking plants on which nematodes can live; volunteer plants from previous crops and weeds usually appear in the field. Thus, factors that reduce the effectiveness of rotation also can apply to fallow. If the field is kept practically free of potential host plants by some combination of chemicals and cultivation, the cost is likely to approach the cost of nematode control by chemical means, and there are likely to be serious losses of soil organic matter and perhaps heavy erosion because of wind storms or heavy rains during prolonged fallow periods.
Crop Destruction. After harvest, destroy roots of the preceding crop as promptly as possible, to interrupt reproduction of nematodes and other pathogens and pests that could otherwise continue to reproduce on the old plants and any weeds that are present. Plowing out roots and shredding crop residues, as by disking, also initiates their decay so that nematodes in them will be exposed to natural control agents in the soil and to nematicides that may be used in the future.
Winter Cover Crops. A small grain cover crop can help prevent growth of weeds that are hosts of peanut nematodes and will help protect the soil from erosion during the winter. However, small grains planted while the soil is warm enough (above 65 o F) for root-knot nematodes to infect new roots may support some nematode reproduction before temperatures drop in winter. Rye, triticale, most varieties of wheat, and barley can support root-knot nematodes; many varieties of oats support less or none. Root-knot nematodes may not increase their numbers in some of these grains, but overwinter decline of the population may be less than wanted. Soil heat units are what drive nematode development. When soils are cool, nematode development slows down; when soils are warm, nematode development increases.
Tillage. Turn the land deeply (12 to 14 inches) at least 4 weeks before fumigation or before final land preparation. This buries surface litter, reducing some fungal diseases, and encourages decay of live plant roots (such as those of a winter cover crop and weeds) that could protect nematodes from their natural enemies or nematicides.
Chemicals should be used where significant nematode problems are present or likely. Nematicides and other soil applied nematicides should be rotated in fields that are to be planted in succeeding crop years. Repeated applications of some soil applied nematicide-insecticides has led to the build up of bacteria and other microbes that rapidly degrade them. The soil fumigant 1,3-dichloropropene must be applied 5 to 7 days before planting; most of the other products can be applied at the time of planting or immediately before. Nonfumigants are more consistent in heavier soils while sandy soils favor fumigation. Many nonfumigants have significant value as soil insecticides, which should be considered when selecting products to use for nematode control. Some nonfumigant nematicides also may be applied at "early pegging time" (or peg initiation) as supplemental treatments to extend control to the time when young peanut pegs and pods are most susceptible to damage.
1,3-dichloropropene (Telone II)- (median $/lb. ai., $1.10) This soil fumigant has often been the most effective nematicide in terms of consistency and yield increases in University of Florida peanut nematode management tests. Experience and formal research in Florida, Alabama, and Georgia have established a few practices that maximize the chance for effective peanut nematode control with Telone:
- It must be used 5 to 7 days preplant; stand reduction, delayed emergence, and early stunting have all been observed when it was applied under the row at or very near to planting time. Do not plant fumigated areas until the odor of Telone is no longer present within the treated zone.
- Inject at least 12 inches below the final soil surface (measured from the bottom of the outlet tube). Row injection at 14 inches deep or greater can lead to treating more soil area with the same amount of applied fumigant. However, do not inject any deeper than the subsoil in soils that have a more dense subsoil that can interfere with free diffusion of fumigant vapors.
- Excellent closure or sealing of treated soil is essential: thin chisels (swept back or forward swept) that place the fumigant 12 inches deep, or thin chisels that follow the coulter, work well for row treatments; deep bottom plow application works well for broadcast applications. One effective way to seal a one- or two-chisel row treatment is to use disk-hillers to throw up a bed 12 to 14 inches high behind the chisel(s), then to remove ("board off") the top of the bed before planting.
- For row treatment, the placement of two chisels spaced 10 inches apart per row works better than a single chisel per row. The two chisels per row permits for a treatment zone of approximately 22 inches wide, which is close to the pegging zone for the peanut.
- Do not apply Telone II when the soil temperature is below 40 degrees F. Soil temperatures best for applying Telone II are 40 to 80 degrees F. Soil moisture should be at ˝ of field capacity, ideal for planting.
- Broadcast application by deep placement with a mold-board plow achieves efficient use of Telone II, providing good control with 9 to 12 gallons per acre. This method of application apparently is efficient because of the complete lack of chisel traces or "chimneys," (normally left by chisels) through which fumes can escape prematurely.
- For heavily infested fields, especially deep sandy soils, broadcast application of nine gallons of Telone per acre followed by a nonfumigant nematicide application at peg initiation often provides the most effective (and cost-effective) treatment. It is applied to approximately 15 percent of the state’s total peanut acreage at a rate of approximately 90 to 120 pounds of a.i. per acre an average of 1.0 time. Telone has a restricted entry interval under the Worker Protection Standard of 5 days.
Nonfumigant Nematicides for Use at Planting
Formulations of ethoprop (Mocap), fenamiphos (Nemacur), aldicarb (Temik), and oxamyl (Vydate) are registered for nematode control. When used at planting, Temik 15G and Nemacur 15G have been the most effective of the nonfumigant products in University of Florida research. Maximum rates of these products have produced yields equal to those obtained with 6 to 9 gal/acre of Telone II applied in the row.
Nonfumigant Granular Nematicides for Application at Peg Initiation to Supplement the Primary Nematicide Treatment
Temik 15G or Mocap 10G may be applied at peg initiation (about 35 to 45 days after planting) to supplement treatment at planting. Such treatments have increased yields 500 to 600 lb/acre in many University of Florida tests. However, these materials may not be applied within 90 days of harvest. Peanut to be harvested early for boiling should not be treated at pegging time with these products. Either Temik 15G or Mocap 10G may be used at peg initiation following a preplant application of Telone II, or an at plant application of Temik 15G, Mocap 10G, or Nemacur 15G. Granules are applied in a 14 to 18 inch band directly over the row. Foliage should be dry when granules are applied, and a weighted burlap bag or similar drag should be pulled over the plants to dislodge granules from the foliage. The granules are incorporated by running sweeps (flat orientation) through the row middles. Granules are applied only when rain is expected or irrigation can be used to dissolve the active ingredients and carry them into the soil within 7 to 10 days. Application is not done during extended dry periods. Foliar sprays of Vydate L also have been effective pegging treatments in some trials (26). Florida law requires that aldicarb users report each use of this material 30 days in advance. This is an added regulatory hurdle that requires planning for compliance. For more details regarding the use of aldicarb refer to the chemical insecticide section above.
Ethoprop (Mocap) - (median $/lb. ai., $12.10) (90 day PHI) Although registered for nematode management in peanut, this product has been a weak nematicide at best and appears to be readily lost by leaching from heavy rainfall in sandy soils typically used for peanut production. It is used very little in peanut production in Florida (26,27). It is applied at a rate of 2 to 3 pounds of a.i. per acre an average of 1 to 2 times. Ethoprop has a restricted entry interval under the Worker Protection Standard of 48 hours.
Fenamiphos (Nemacur) - (median $/lb. ai., $20.67) Producers who use an at-planting non-fumigant nematicide sometimes prefer fenamiphos to aldicarb simply because there is no requirement to register each use with the Department of Agriculture and Consumer Services. Fenamiphos generally is more efficacious when used in slightly heavier soils. Fenamiphos is not registered for post-planting use (26,27). It is applied at a rate of approximately 1.5 to 2.5 pounds of a.i. per acre an average of 1.0 time. Fenamiphos has a restricted entry interval under the Worker Protection Standard of 48 hours.
Oxamyl (Vydate) - (median $/lb. ai., $31.88) Oxamyl is typically ineffective under Florida conditions when used to treat soil directly at planting. Oxamyl sometimes has partially suppressed nematode activity later in the season when applied in two foliar sprays at peg initiation (26,27). It is applied at a rate of approximately 1 pound of a.i. per acre an average of 1 to 2 times. Oxamyl has a restricted entry interval under the Worker Protection Standard of 48 hours.
Department of Agronomy
University of Florida
Gainesville, FL 32611
North FL REC - Quincy
University of Florida
30 Research Rd.
Quincy, FL 32351
Department of Plant Pathology
University of Florida
Gainesville, FL 32611
Entomology and Nematology Department
University of Florida
Gainesville, FL 32611
(352) 392-1901 ext. 135
Florida Farm Bureau
Gainesville, FL 32614
(352) 378-8100 ext. 1545