Crop Profile for Peanuts in Alabama

Prepared: September, 1999
Revised: August, 2000

General Production Information


Production Regions

Peanuts were grown in 15 Alabama counties, however, most production occurred in eight counties in southeast Alabama: Houston, Henry, Geneva, Coffee, Barbour, Dale, Pike and Covington. (3)


Production Practices



Insect Pests

IPM Program:

Approximately 65% of peanut growers use pest threshold guidelines for application of insecticides, and 74% of growers apply pesticides as needed rather than on a routine schedule. (7)

Resistance Management Programs:

Approximately 22% of growers alternate different classes of pesticides to reduce build-up of resistance by pests. (7)

Efficacy Issues:

Biological Controls:

A majority of growers chose insecticides less damaging to beneficial insects, and approximately 73% of growers use the lowest recommended rates to help preserve beneficials. Other than Bacillus thuringiensis insecticides, biological controls are not directly used for insect control. (7)

Other Issues:

Evaluations of newer insecticides with reduced environmental/toxicity profiles are being conducted to evaluate their efficacy for foliage feeding insect pests. Several of these currently under study are spinosad (Tracer), Emamectin benzoate (Denim) and Indoxicarb (Steward). Adoption of the use of these materials as replacements will be contingent on the manufacturer’s ability to register them.

Variety evaluations are being conducted to determine their tolerance to the major insect pests of peanuts. Tillage studies continue to evaluate the effects of a minimum tillage system on reductions of thrips population and tomato spotted wilt virus. So far any reductions in pest damage due to changes in tillage or variety have been in the 10-15% range and alone, without additional management inputs, would not be sufficient to prevent economic losses to these insect pests.


Thrips

Thrips was the most serious insect threat to Alabama peanut crops in 1996. About 82% of the acreage received insecticide treatment for thrips. (5)

Thrips are tiny, slender insects that jump or fly around when disturbed. (10) Four species of thrips have been found to occur commonly on peanuts in Alabama. Tobacco thrips, Frankliniella fusca (Hinds), is the most abundant. The adults are tiny, slender insects barely visible to the unaided eye. They may vary in color from dark brown to yellow. The immatures are even smaller and are generally yellow.

Thrips adults and immatures primarily cause damage to peanuts by feeding on seedling plants. They feed in the folded leaflets of the buds of plants causing scarred, deformed leaves, which are often referred to as "possum-eared." Tobacco thrips and the less common western flower thrips are also vectors of the tomato spotted wilt virus (TSWV) in peanuts. Since 1986, TSWV has infected peanut crops in Alabama at low levels. Some TSWV-infected plants can be found in most fields, but significant yield losses have not occurred due to TSWV.

As soon as peanuts emerge from the soil after planting, adult thrips may be found feeding in the terminals. Eggs are laid in the terminal bud and within a week, small, yellow immature thrips may be seen in the folded bud leaves. As these leaves grow and unfold, the scarring from thrips feeding is evident. The severity of thrips damage to peanuts is related to the number of thrips feeding and the growth rate of the peanut seedling. The most severe thrips damage occurs in the earliest plantings and damage usually declines as the growing season progresses.

Healthy peanuts can recover from thrips damage with minimal effect on yield; but the other early season stresses, including herbicide injury, dry weather and cold soil, can combine with thrips damage so that a delay in maturity and yield loss may occur.

Since all peanut plants in a field will be uniformly infested with thrips, preventative insecticide treatments provide the greatest protection from thrips damage. (11)

Chemical Controls:

Good thrips control requires preventive treatment. The most common means for control is the use of an at-plant, in-furrow insecticide used in a preventive manner. Products recommended for this practice include:

organophosphate insecticides

carbamate insecticides

Efficacy Issues:


Tomato Spotted Wilt Virus (TSWV)

To control thrips vectors of TSWV, use a granular systemic insecticide in or to the side of the seed-furrow at planting, or make two foliar applications of insecticides at 14-day intervals beginning at the first sign of thrips damage. (10)

Foliar applications of insecticides for thrips control will not significantly reduce TSW levels and can destroy beneficial populations. For growers with peanut fields that have high levels of TSW, variety selection and combinations of other cultural practices are the only recommended management measures. Avoid especially early planting (mid-April) and plant normal to high seeding rates (85-100 pounds per acre) where TSW is a problem. (8) [See also Plant Diseases section on TSWV.]

Alternatives:

Planting of peanut cultivars with resistance to tomato spotted wilt virus and planting in a time window of May 1 though May 15 are effective methods to reduce the incidence of tomato spotted wilt disease by avoiding heavy thrips populations.

Soil application of phorate is used as an effective alternative to foliar sprays of Orthene or Karate for thrips and tomato spotted wilt virus control. This results in less impact on nontarget organisms and decreased incidence of disease. Phorate is effective only when TSW pressure is very high.

Cultural Control Practices:


Lesser Cornstalk Borer

One of the most serious soil-inhabiting insect pests of peanuts in Alabama is the lesser cornstalk borer. About 19% of the acreage received insecticide treatment for lesser cornstalk borer in 1996. (5) Lesser cornstalk borers are dark, blue-green larvae ranging from 1/2 to 3/4 inch in length with brown or purple bands around their bodies. They feed on leaves, pegs and pods; bore into the plant near the soil line; and tunnel throughout roots and stems. They live in silken tubes or webs on or just beneath the soil surface. These tubes are usually attached to the plant wherever the insect is feeding. Damage is more common on light sandy soils and is usually more severe in hot, dry weather. (10)

The lesser cornstalk borer is an insect in the Order Lepidoptera and has four life stages: egg, larval, pupal and adult. Eggs are laid singly or in small groups within 1/4 inch of the soil surface under the peanut canopy. These eggs are white when they are first laid and turn red just before hatching. The adult moth "glues" these eggs to sand particles when the soil is moist. Newly emerged larvae crawl across the soil surface or on the plant and locate suitable host plant parts for feeding. Lesser cornstalk borer larvae molt six times and increase in size with each molt. Larvae are easily recognized by the bluish-green bands on their bodies and by their violent wiggling when disturbed. Larvae spend most, but not all, of their time below the soil surface or inside of plant stems. Many larvae will typically construct a silken tube that is interwoven with soil particles and is attached to the plant. Silken tubes can usually be found either attached to the plant, on the soil surface or within the top 1/2 inch of the soil surface.

The pupae are small and brown, with few markings. Pupation also occurs in the soil, so most of the life cycle of this insect is spent underground.

Adults are small moths that are about 1/2 inch long. Males are tan in color with a dark grey stripe on interior edges of their wings. Females are dark grey in color and may possess a metallic sheen. They are less active in the heat of the day, although moths are easily found during the day in years with population outbreaks. Females are harder to locate than are males due to their dusky coloration and their unwillingness to fly.

Population outbreaks typically occur during hot, dry weather in peanuts grown in sandy soils. These outbreaks can be either sporadic and occur only where hot and dry conditions prevail, or they can be widespread. When widespread, the lesser cornstalk borer can be devastating to most peanuts in the Southeast. (9)

Chemical Controls:

Fields should be closely checked for fresh feeding signs and the presence of borers. Control is needed when fresh damage or borers are found at 30% of sites scouted in a field. (13) At the first sign of a general infestation, an application of a recommended granular insecticide should be made. It should be applied in a 16- to 18-inch band over the row when the foliage is dry so the insecticide granules will filter down to the soil surface. Light to moderate rainfall or an application of irrigation water following treatment will improve control. (10)

The only labeled material available in 1996 for control of lesser cornstalk borer in peanuts was chlorpyrifos (Lorsban 15G) (an organophosphate insecticide). About 8% of the peanut production acreage was treated with chlorpyrifos, used at 2 pounds of active ingredient per acre. (5) The product is applied once at midseason.

Efficacy Issues:

Lorsban is the only soil insecticide available and provides moderate control of lesser cornstalk borer, southern corn rootworm and wireworms.


Spider Mites

Insecticide was used to treat spider mites in almost 9% of the acreage in 1996 in Alabama. (5) The predominate spider mite found on Alabama peanuts is the two-spotted mite. These tiny, insect-related pests feed primarily by sucking juices from the undersides of the leaf. The feeding causes very small yellow speckling on the upper surface of the leaves. The leaves then gradually become chlorotic, turn brown and die. Large populations of mites can be solely responsible for serious plant damage and defoliation. There is usually some very fine webbing found where spider mites feed. (11)

The mites themselves are yellow with two black spots on the body. Immatures appear to be red or reddish-yellow. Adults lay eggs near the underside of the leaflet midvein. As the population increases, they begin to move to the terminals of the plant with "balls" of mites accumulating at the top of the plant. (11)

Spider mites usually migrate from weedy field borders, utility poles or garden areas. In the heat of the summer, as these areas begin to dry up, the mites are spread by wind, equipment or animals moving through the peanuts. Therefore, initial infestations are usually small and spotty, limited to areas 2 to 3 feet in diameter. Early infestations of spider mites may be confused with damage caused by peanut rust. (11)

Spider mites represent a significant threat to peanuts because of their potential to build up to a high population before they are detected and the high cost and inability to achieve control. Uncontrolled populations of spider mites can completely defoliate peanuts and cause significant yield loss in the affected area.

Chemical Controls:

Scouts should be alert to look for symptoms of mite infestation before they spread over the field. In general, spider mites are hot, dry weather pests with major outbreaks occurring in droughty years. Applications of certain foliar insecticides may also "trigger" outbreaks of mites if weather conditions are favorable. Most insecticides will not effectively control these pests and an effective miticide must be used to obtain effective results. (11)

Only two registered products were available for control of spider mites in peanuts: propargite (Comite 6.55 and Omite 30W). In some cases, a pyrethroid insecticide (Karate) may have been used for light infestation to suppress populations. Both products often require two applications to obtain good control (recommended no more than twice per season; may cause foliar burn, especially if temperature is greater than 90 degrees F). (13)

Controls are often applied after populations have far exceeded tolerable levels, primarily because the small size of the pest allows it to go undetected until severe damage suddenly appears. Propargite is relatively nontoxic to off-target organisms. The availability of these two products is critical for resistance management.

Alternatives:

Alternative cultural methods of control include avoiding the use of insecticides when conditions are hot and dry, not mowing field borders and frequent scouting to pinpoint early infestation of spider mites.


Corn Earworm, Fall Armyworm, Cutworm and Related Lepidoptera Pests

Foliage-feeding caterpillars are destructive insects that feed on peanut leaves as they grow and develop into adult moths. The full-grown worms, the fifth and sixth larval stages, consume the most foliage and are usually the most difficult to control with insecticides. About 46% of the acreage in 1996 was treated for corn earworm, fall armyworm, beet armyworm and velvetbean caterpillars. (14)

Peanut foliage-feeders vary considerably in their susceptibility to insecticides. Therefore, the peanut grower or the scout must be able to correctly identify the caterpillars.

Corn earworms vary in color from light green to almost black. They are one of the most common caterpillars that feed on peanut foliage. The life cycle requires about 30 days, with 14 to 16 days of this time spent in the larval stage. Several generations may occur in peanuts during a single growing season. Corn earworms usually are controlled by the use of insecticides.

Fall armyworms are multi-colored, striped larvae usually having a light-colored inverted "Y" on the head. The life cycle requires about 30 days with about half of this time spent in the larval stage. There may be several generations during a year. They feed on the foliage of peanut plants. This pest can be effectively controlled by the use of a recommended insecticidal spray.

Granulate cutworms are fat, tan to dark-colored caterpillars. They are often called "night-crawlers." They hide under trash, in cracks or below the soil surface during the day. Occasionally, they cut young plants off at or below the soil surface and feed on pods and pegs. However, their primary damage is caused when they climb the plants and feed on the foliage. At times these pests are present in large numbers and seem to be causing little or no damage. When they begin to feed on the foliage, they may cause significant defoliation. Foliage feeding usually occurs at night and the "worms" return to the soil during the day. Cutworms can be controlled with recommended foliar-applied insecticides.

Velvetbean caterpillars are green to black larvae that usually have white stripes the length of the body. These larvae are very active when disturbed. They feed on the foliage and may completely strip plants of all leaves and destroy the terminal buds. Development from egg to adult requires 4 to 5 weeks. The destructive larval stage usually lasts from 16 to 21 days. Two or three generations may occur late in the peanut growing season. This insect is very easily controlled with recommended insecticidal sprays.

Beet armyworms are sporadic pests of peanuts. They feed on plant foliage. They are quite variable in color but always have a dark stripe down the middle of the back and two light yellow stripes down each side. There is usually a small black spot on each side above the second pair of true legs just behind the head. This caterpillar is mature when it is slightly more than 1 inch long. Beet armyworms are very difficult to control with insecticides. (10)

Chemical Controls:

Peanut plants are extremely resilient, having the ability to recover from all types of stresses, including defoliation from insects. However, there is a point at which defoliation will lower yield. On the average, 30% is the maximum defoliation allowable to prevent yield or quality loss. Peanuts are most sensitive to yield loss by defoliation at 75 to 85 days after planting or during the peak pod-fill stage. Depending upon variety and weather factors, these time periods may shift from one year to the next. (14)

Treatments to control foliage feeders on peanuts are recommended based on the number of caterpillars per linear row foot, not defoliation. Observations and experience have shown that levels of caterpillars less than 4 to 6 per row foot generally will not cause more than 30% defoliation under normal growing conditions. (14)

Control of these pests is achieved with the use of foliar insecticide sprays.

Available foliar insecticide sprays include:

carbamate insecticides

organophosphate insecticides

pyrethroid insecticides

bacillus thuringiensis insecticides, all used to control corn velvetbean caterpillars and green cloverworms. A delay in larval mortality may occur. Use on small- to medium-size larvae. At high population levels, a contact insecticide should be added.

Insecticides used in early or mid season may cause larger populations of foliage-feeding caterpillars later in the season because of the destruction of beneficial insects that help control these caterpillars. (13, 8)

The different species of foliage feeders vary in their susceptibility to the insecticides above. Therefore, the particular foliage feeder species present in a particular field will determine the selection of the insecticide. It is important to maintain several classes of chemistry to obtain control of all the various species in all Alabama fields.

Efficacy Issues:



Weeds

Nearly all the peanut acreage in Alabama is infested with one or more species of weeds. Weeds are estimated to cost peanut producers $183 per acre, resulting in a total loss of $35,136,000 for the 1996 crop season.

The weeds that are problematic are generally lumped into three groups: the nutsedges, grasses and broadleaves.


Nutsedges

In 1996, producers treated 88.3% of the surveyed acreage for nutsedges. (5) The nutsedges include yellow and purple nutsedge. Nutsedges are herbaceous perennials in that they regrow each year from soilborne tubers. Tuber germination occurs sporadically over time due to dormancy. Dormant tubers are immune to herbicides. Furthermore, the foliage of actively growing nutsedges is very waxy and is held in a near vertical position. Thus herbicide absorption is minimal.

Chemical Controls:

Until recently control was obtained with soil-applied herbicides that included the thiocarbamates (i.e., vernolate, Vernam 7E) and the chloroacetamides (i.e., alachlor, Lasso EC and metolachlor, Dual 8E). Unfortunately, control was generally variable and never complete.

In the last few years, imazapic (Cadre DG) has been registered for use in peanuts. Imazapic has provided a new level of control of nutsedge as well as excellent control of several grass and broadleaf weeds. Imazapic is applied early postemergence and enters the target weeds through both the roots and shoots. Unfortunately, imazapic is relatively long lived in the soil and its use prohibits recropping to cotton.


Grasses

Problematic grasses include several species of which large crabgrass, Texas panicum, Bermudagrass, Fall panicum and Johnsongrass were the most prevalent and widespread. (5) When left uncontrolled, these grasses can bind the peanuts that are produced in a sod-like mat of roots. Thus grass control is critical for production.

Chemical Controls:

The mainstay for the control of these species has been the dinitroaniline herbicides such as pendimethalin (Prowl 3.3E) and ethalfluralin (Sonalan 3EC). These herbicides inhibit root development, thus germinating seeds do not become established. Grass species that have relatively large seeds (Texas panicum is a perfect example) can frequently germinate from beneath the treated soil. The chloroacetamides are also effective in controlling annual grasses. The postemergence-applied, grass-active herbicides such as sethoxydim (Poast Plus 1E) and clethodim (Select 2EC) are very effective in controlling annual grasses.


Broadleaves

Broadleaf weed species most prevalent in Alabama include Florida beggarweed, cocklebur, sicklepod, Florida pusley, Bristly starbur, ragweed, pigweed and several species of annual morningglory. (5) In addition to competition for light, water and nutrients, these tall-growing species frequently tower above the peanut canopy and prevent fungicide application from reaching the peanut foliage. Thus, control of these species is seen as a prerequisite for obtaining disease control.

Chemical Controls:

Several options are available for the control of these species. All the previously mentioned herbicides have some broadleaf activity. In particular, imazapic (Cadre DG) is effective against a number of broadleaf species. In addition, 2,4-DB (Butyrac), which is applied postemergence, is effective against sicklepod and most annual morningglories.

Paraquat (Starfire 1.5) is generally considered to be a nonselective herbicide, but can be used selectively in peanuts. The key for obtaining selectivity is the use of relatively low rates (i.e., <0.13 lb./a) and an early season application (i.e., within 21 days of emergence). This very inexpensive treatment is effective in controlling a diverse group of weed species. The injury that is inflicted on the peanut is transitory and not reflected in yield.

Paraquat can be supplemented with 2,4-DB and/or bentazon (Basagran 4). Bentazon applications tend to reduce the paraquat-induced injury to peanut and also contribute activity toward the nutsedges.

The herbicide pyridate (Tough) is also registered for the postemergence control of Florida beggarweed.

The final option during the growing season for the control of broadleaf weeds is the late season application of chlorimuron (Classic 25DF). This treatment is unique in that peanut plants are not tolerant of Classic until very late in the season. This treatment is particularly effective in controlling Florida beggarweed.


Herbicide group classification

Herbicides used in peanuts may be classified into three groups on the basis of time at which these materials are applied. These groups are preplant soil incorporated, preemergence and postemergence treatments.

Preplant soil incorporated treatments

Herbicides in this group must be thoroughly incorporated into the soil soon after they are applied to prevent loss of activity. The optimum incorporation depth and the amount of delay time possible between application and soil incorporation varies with the herbicide.

Preemergence treatments

Preemergence herbicides are applied at planting or after planting, but before peanuts emerge. This treatment can be applied broadcast across the entire field or in a band beside the rows. Granular application in a band is more popular. Consistent control depends upon moisture, rainfall or irrigation for activation of the herbicide.

Postemergence treatments

Depending upon the herbicide, postemergence treatments may be applied from after ground cracking to approximately 40 days before harvest. Early-season postemergence herbicide applications are the most effective means of controlling sicklepod, Florida beggarweed, cocklebur and bristly starbur in peanuts.

Where preplant soil-incorporated or preemergence herbicides are applied as preventive treatments, postemergence treatments are applied only after a weed problem develops. The time of postemergence herbicide applications is critical. To obtain effective results, these herbicides must be applied when weeds are small, usually less than 2 inches in height, and actively growing. Results are usually poor if treatments are applied to large, well-established weeds or to weeds that are not actively growing.

Weed control in peanuts often requires the use of sequential preplant, preemergence or postemergence herbicides. However, research indicates that the intensive use of herbicides may result in peanut injury. The combined effect of environmental stresses, soilborne diseases, nematode injury and herbicide injury may cause significant reductions in peanut vigor and yield. (10)

Cultural Control Practices:

Cultural practices can reduce weed competition. Some of the practices that are used in peanuts (but are not limited to peanuts) include 1) manipulating row spacing, 2) manipulating the planting date, 3) crop rotation and 4) cultivation.

Peanuts are normally planted in rows spaced approximately 36 inches apart. This spacing is largely traditional, having its origin in the space required for the passage of mules. While some type of a row orientation is required for machinery movement, a twin row design has been demonstrated to enhance crop performance. In this design the single row is replaced with two rows that are 5 to 7 inches apart. Total plant population, on a per acre basis, remains the same. Yields from twin row design are generally slightly higher than the traditional row arrangement. It follows that since the distance between rows is less, the peanut crop develops a canopy over the site quicker. This should be beneficial to weed control. Unfortunately, this benefit is small since research has shown that the twin row design does not allow for any reduction in weed control inputs, such as herbicides.

Peanuts mature over a relatively long growing season of approximately 140 days. Furthermore, peanuts require a soil temperature of at least 80 F to germinate. Thus to be successful, peanuts must be planted within a period that is no more than 4 weeks in length. But even with this limited flexibility in planting date, it has been noted that weed problems can be altered whether peanuts are planted at the start or the end of this period. The most celebrated example is with Texas panicum. It is generally believed that early planting allows the peanuts to "get the jump" on this most difficult to control weed. In addition, a fast maturing variety can avoid late season weed problems. But, as with all these cultural practices, the direct benefit on weed control is very subtle and hard to measure.

Peanuts are generally not planted to a common location for more than two consecutive seasons due to disease build up. Rotating to a none legume crop, preferably a grass-type crop such as corn or pasture, is desirable for overall disease management. In addition, weed problems can often be successfully addressed during these rotational crops. Generally, peanut production promotes the accumulation of weed species that are taxonomically similar to the crop and/or perennials. Thus, continual peanut production promotes the proliferation of legume weeds and/or nutsedges. These weeds often can be more effectively controlled in the rotational crop than in the peanut crop. When peanuts are again planted on the site, weed pressure is generally markedly reduced.

Cultivation remains the most well established and effective cultural method of weed control. The only limitation is that care must be taken to limit moving soil only, since disturbing the peanut foliage can promote soilborne diseases.

Weed mowing, a novel cultural practice, has been recently investigated by the authors. The intent was to replace herbicide inputs with the periodic mowing of any weed foliage that extended above the peanut canopy. While mowing reduced the visual impact of tall rank-growing weeds, weed-induced yield loss could not be restored. Highest yield and net returns were consistently obtained with a comprehensive, herbicide-based weed control program. Conversely, mowing was beneficial only in situations where no other weed control inputs had been used, i.e., salvage-type situations.

Peanut production in Alabama remains dependent on chemical inputs to control weeds. Any future reduction in this dependency remains unlikely.

IPM programs:

Although most peanut growers use pre- and postemergence herbicides, 54% use mechanical weeding to help manage weeds. Approximately 28% scout fields in the fall for weeds, and 95% scout fields during the growing season to determine timing of postemergence herbicides. (7)

Alternatives:

In Alabama, 54% of growers use mechanical weeding to help manage weeds and 80% rotate fields with other crops to aid in weed management. (7)


1996 Alabama Herbicide Usage Information

The following data was derived from the Alabama 1996 Statewide Peanut Producer Survey conducted by the Alabama Agricultural Statistics Service for the Alabama Pesticide Impact Assessment Program.

Weed Prevalence

Weed
(common name)

Survey
Percentage

Weed
(common name)

Survey
Percentage

Nutsedge

88.3

Fall Panicum

34.1

Florida Beggarweed

87.7

Johnsongrass

33.1

Morningglory

86.7

Bur Gherkin

31.5

Cocklebur

85.6

Tropic Croton

25.6

Crabgrass

78.4

Wild Poinsettia

22.0

Bristly Starbur

77.0

Lambsquarter

20.1

Sicklepod

75.0

Broadleaf Signalgrass

13.1

Florida Pusley

71.8

Crowfootgrass

12.8

Texas Panicum

68.7

Crotalaria

12.2

Ragweed

55.7

Jimsonweed

10.8

Bermudagrass

49.2

Redweed

9.1

Pigweed

48.0

Wooly Croton

8.0

Wild Citron

38.0

Goosegrass

3.9

Prickly Sida

34.7

Preplant Herbicides

Herbicide Trade Name (Rate/Acre Broadcast)

Herbicide Common Name (Active Herbicide/Acre)

Acres Treated

Total Product Applied1

Sonalan 3EC (2 pt.)

Ethalfluralin (0.6-1.125 lb.)

91,584

22,896 gal.

Prowl 3.3E (1.8 pt.)

Pendimethalin (0.75-1 lb.)

73,152

16,459 gal.

Dual 8E (2 pt.)

Metolachlor (1.5-2 lb.)

66,624

16,656 gal.

Pursuit 70DG (1.4 oz.)

Imazethapyr (0.0625 lb.)

8,064

706 lb.

Vernam (2 1/3 pt.)

Vernolate (2-2.625 lb.)

5,568

1,624 gal.

Frontier 6E (1.5 pt.)

Dimethenamid (1.18-1.5 lb.)

822

154 gal.

1 Total product applied was calculated on the average label rate.

Preemergence Herbicides

Herbicide Trade Name (Rate/Acre Broadcast)

Herbicide Common Name (Active Herbicide/Acre)

Acres Treated

Total Product Applied1

Prowl 3.3E (1.8 pt.)

Pendimethalin (0.75-1 lb.)

11,904

2,678 gal.

Dual 8E (2 pt.)

Metolachlor (1.5-2 lb.)

5,376

1,344 gal.

Pursuit 70DG (1.4 oz.)

Imazethapyr (0.0625 lb.)

2,880

252 lb.

1Total product applied was calculated on the average label rate.

Postemergence Herbicides

Herbicide Trade Name (Rate/Acre Broadcast)

Herbicide Common Name (Active Herbicide/Acre)

Acres Treated

Total Product Applied1

Butyrac 200 (0.2 lb.)

2,4-DB (0.2-0.25 lb.)

108,288

10,829 gal.

Starfire 1.5 (0.6875 pt.)

Paraquat (0.125 lb. + non-ionic surfactant

99,456

8,547 gal.

Cadre DG (1.44 oz.)

Imazameth (0.063 lb.) + non-ionic surfactant

74,304

6,502 lb.

Classic 25DF (0.5 oz.)

Chlorimuron (0.125 oz.)

45,504

1,422 lb.

Basagran 4 (2 pt.)

Bentazon (0.75-1 lb.)

42,048

10,512 gal.

Storm (1.5 pt.) + crop oil concentrate (2 pt.)

Bentazon (0.5 lb.) + aciflurofen (0.25 lb.) + crop oil concentrate

32,448

6,084 gal.

Dual 8E (2 pt.)

Metolachlor (1.5-2 lb.)

18,048

4,512 gal.

Blazer 2L (1.5 pt.)

Aciflurofen (0.5 lb.) + non-ionic surfactant

14,400

2,700 gal.

Poast Plus 1E (1.5 pt.) + crop oil concentrate (2 pt.)

Sethoxydim (0.2 lb.) + crop oil concentrate

13,440

2,520 gal.

Prowl 3.3E (1.8 pt.)

Pendimethalin (0.75-1 lb.)

11,712

2,635 gal.

Pursuit 70DG (1.4 oz.)

Imazethapyr (0.0625 lb.)

3,072

269 lb.

Tough (2 pt.) + Butyrac 200 (0.8 pt.)

Pyridate (0.94 lb.) + 2,4-DB (0.2 lb.)

1,880

470 gal.

1Total product applied was calculated on the average label rate.



Diseases

Diseases and nematodes are major factors that limit the size, quality and profitability of peanut production in Alabama. Alabama’s hot, often wet summer weather favors the development of destructive outbreaks of disease and nematode pests. In addition, rotation patterns practiced on the majority of Alabama’s peanut farms often favor the establishment of damaging populations of soilborne plant pathogens and plant parasitic nematodes. Finally, production practices such as irrigation, tillage practices and cultivar selection also play a significant role in the onset and severity of diseases and nematode pests on peanut. Early and late leaf spot, southern stem rot (white mold), and the peanut root-knot nematode are the most common and damaging diseases on Alabama’s peanut crop. Other damaging diseases include seedling diseases, peanut rust, Rhizoctonia and the virus disease tomato spotted wilt (TSWV).

Disease control inputs are a sizable portion (25% or more) of the variable costs in the production budgets on many Alabama farms. According to a 1996 survey, approximately 92% of Alabama’s peanut acreage was treated with a fungicide or a fumigant nematicide for the control of one or more diseases or nematode pests. The majority of Alabama’s peanut acreage (an estimated 177,622 acres) received multiple treatments of one or more fungicides such as chlorothalonil, tebuconazole or propiconazole for the control of early and late leaf spot as well as peanut rust. More than half the acreage (an estimated 125,026 acres) was also treated with tebuconazole, flutolanil or chlorpyrifos for the control of southern stem rot (white mold) and Rhizoctonia limb rot. Finally, 68,544 acres were treated with the nematicide aldicarb to control the peanut root-knot nematode. (5)

With the notable exceptions of leaf spot diseases, fungicide and nematicide treatments are generally applied on the basis of field history. Typically, leaf spot fungicides are applied preventatively on a 14-day calendar schedule. A total of six or seven fungicide applications are required to control leaf spot diseases and peanut rust. The AU-Pnut leaf spot advisory is available to peanut producers but has not been widely utilized. Implementation of an expert system such as AU-Pnut potentially can save from 1 to 3 fungicide applications per year. Only 12.4% of respondents, however, indicated that they use disease forecasts to schedule fungicide applications. (7) Difficulty in monitoring daily rainfall in widely scattered fields as well as problems with making timely fungicide applications has limited the adoption of AU-Pnut. An on-line interactive version of AU-Pnut, which utilizes Doppler Radar to measure rainfall, is now being field-tested by selected Alabama growers. Generally, the fungicides used to control southern stem rot either have good activity against leaf spot diseases and peanut rust or are applied in combination with a fungicide that will control foliar diseases. Only a relatively small percentage of Alabama’s peanut acreage is treated for peanut root-knot nematode on the basis of a nematode soil assay. In most cases, nematicide use is determined on the basis of cropping history or on recollection of injury to the previous peanut crop.

Major diseases of peanut include early and late leaf spot, peanut rust, southern stem rot, Rhizoctonia limb rot, peanut root-knot nematode and the virus disease tomato spotted wilt.


Early and Late Leaf Spot

Early and late leaf spot are common and potentially destructive diseases of peanut. Currently, early leaf spot is the most common leaf spot disease on peanut. Between 1979 and 1990, late leaf spot, however, caused significant yield losses. When left uncontrolled, potential losses to one or both of these diseases can easily exceed 50% or more of anticipated yields. For decades, peanut harvesting started when the peanuts in a field were stripped of their leaves by one of these diseases. Greatly improved disease control in the early 1970s, which followed the introduction of more effective leaf spot fungicides, resulted in sizable yield gains. Currently, annual yield loss attributed to these diseases usually ranges from 5% to 7%. Heaviest losses in pod yield and grade are typically seen when summer weather patterns are wet and hot.

Both diseases are characterized by the appearance of circular brown spots or lesions on the leaves. Symptoms may be first seen within three weeks of seedling emergence. During periods of wet weather, disease spreads rapidly through the peanut canopy. Heavily spotted leaves quickly yellow and fall to the ground. The earlier leaf shed begins, the greater the loss in pod yield.

Cultural Controls:

Crop rotation will delay disease onset by reducing inoculum carryover on peanut crop debris. Approximately 80% of peanut producers surveyed rotated peanuts with other crops. Corn and cotton are the crops most often rotated with peanut. (7) Cropping peanut behind one year of another crop, which has limited impact on leaf spot pathogen survival, is the most common rotation pattern. On a sizable acreage, peanuts are often cropped for several consecutive years. A small percentage of Alabama’s peanut crop is planted behind two years of corn, cotton or a pasturegrass.

Turning under the debris of the previous peanut crop with a moldboard plow has long been recommended as a method of slowing disease spread early in the growing season. However, reduced tillage practices have been adopted within the past year on an estimated 30% of Alabama’s peanut acreage. The impact of reduced tillage practices on the onset and development of leaf spot diseases is unknown.

Historically, commercial runner-type peanut cultivars had little if any resistance to leaf spot diseases, although a few appeared especially sensitive to early leaf spot. Within the last decade, three runner-type peanut cultivars with partial resistance to early and late leaf spot have been released and have been widely adopted by producers. In Alabama’s wet, humid climate, the level of resistance now available is insufficient to safely reduce the number of fungicide sprays without jeopardizing peanut yields and crop quality. (17)

Chemical Controls:

Fungicides are required to protect peanuts from leaf spot diseases and produce acceptable crop yields. Typically, applications are made on a calendar basis every 10 to 14 days until 2 weeks before harvest. During extended periods of dry weather, producers may delay fungicide applications until after a soaking rain. The weather based spray advisory AU-Pnut is available to producers but has been difficult for peanut producers to implement.

Chlorothalonil, which is marketed under the trade names Bravo 720 Weather Stik, Bravo Ultrex, Echo 720 and Terranil, is the most widely used fungicide for the control of early and late leaf spot control on peanuts. In 1996, approximately 3 to 4 applications of a chlorothalonil fungicide were made to 90% of Alabama’s peanut acreage. Prior to the registration of Folicur 3.6F and Abound 2SC, up to 8 or more applications of a chlorothalonil fungicide were made per year for the control of leaf spot diseases of peanut. Efficacy of chlorothalonil fungicides against early and late leaf spot disease as well as peanut rust is quite good. If disease is severe, peanut producers are advised to shorten the spray interval from the recommended 10 to 14 days to as little as 7 days.

Chlorothalonil is also a critical component in the resistance management programs for triazole and strobilurin fungicides on peanut and other crops. Experience with benomyl on peanuts in the early 1970s has clearly demonstrated that populations of the causal fungi of early and late leaf spot have the potential to rapidly develop resistance to single site inhibitors, such as newly released triazole and strobilurin fungicides. Resistance to both triazole and strobilurin fungicides has been reported in Europe. Failure to employ a nonselective multisite inhibitor such as chlorothalonil when using a triazole or strobilurin fungicide could result in a catastrophic control failure and sizable yield loss. Currently, FRAC guidelines state that a triazole fungicide should total no more than half of all applications made to peanut per year. If more applications of any triazole fungicides are planned in one growing season to a given field, growers are strongly advised to tank-mix 0.5 to 1.0 pints of Bravo 720 or an equivalent with all triazole fungicides. (8) With the probable registration of additional strobilurin fungicides on peanut, similar guidelines will have to be followed for this class of fungicides.

Tebuconazole (triazole) is currently marketed on peanut as Folicur 3.6F. The FolicurCL twin-pack of Folicur 3.6F and Bayer 720 (chlorothalonil) was only sold during the 1996 growing season. When a block of four successive sprays are applied every 10 to 14 days, this fungicide will give good control of both leaf spot diseases. Typically, from 3 to 4 consecutive applications of Folicur 3.6F are applied at the beginning in late June or early July. According to the 1996 survey, an average of 3.1 and 3.8 applications of Folicur 3.6F and Folicur CL, respectively, were made to a total of 57.3% of Alabama peanut crop. (5) Currently, Folicur 3.6F is also widely used for the control of early and late leaf spot and has excellent activity against peanut rust, southern stem rot and Rhizoctonia limb rot. For season-long control of leaf spot diseases, the block spray program for Folicur 3.6F is preceded and then followed by 2 applications and then a single application, respectively, of a chlorothalonil fungicide. The block spray program of Folicur 3.6F gives excellent control of leaf spot diseases of peanut and the protection provided by this fungicide will last until harvest.

Azoxystrobin (strobilurin), which was released in 1997 and not included in the 1996 survey, is marketed on peanuts as Abound 2SC. Two broadcast applications of Abound 2SC at 18.5 to 24.6 fluid ounces per acre, which should be made approximately 60 and 90 days after planting, are targeted mainly for the control of southern stem rot and Rhizoctonia limb rot. Abound 2SC, however, also has good activity against early and late leaf spot. To ensure season-long leaf spot and rust control, apply the recommended rate of a chlorothalonil fungicide at 10- to 14-day intervals, before and after applying Abound 2SC.

Propiconazole [Tilt 3.6E and Tilt 45W] (triazole) is also applied with a chlorothalonil tank-mix partner in late spring primarily for the control of early leaf spot. This fungicide must be applied at the highest label rates for the control of late leaf spot and may be ineffective against peanut rust, southern stem rot and limb rot. Application interval for Tilt/chlorothalonil combinations is 10 to 14 days. For the 1996-growing season, 21.4% of Alabama’s peanut acreage was treated with this fungicide. (5)

Other fungicides available but rarely used on peanut for the control of leaf spot diseases in Alabama include Benlate, Copper, Kocide 101, Flowable sulfur and Topsin-M. Efficacy of these fungicides against early and late leaf spot is inferior to that of all chlorothalonil fungicides, tebuconazole and azoxystrobin. (8, 17)

Table 1. Use pattern for fungicides applied for the control of early and late leaf spot on peanut according to the Alabama 1996 Statewide Peanut Producer Survey

Fungicide

% Survey Acres
Treated

Avg. No.
Sprays

Fungicide

% Survey Acres
Treated

Avg. No.
Sprays

Benlate

< 1

<1

Folicur 3.6F

41.2

3.1

Bravo 720 6F

45.3

3.6

Folicur CL1

16.1

3.8

Bravo Ultrex

5.6

2.0

Kocide 101

0

0

Echo 720

10.3

3.1

Manzate

0

0

Copper

0

0

Sulfur

3.1

1.8

Dithane

0

0

Topsin-M

0

0

Evade1

9.0

3.0

Terranil

27.8

3.9

Tilt 3.6E

21.4

1.5

Other

.249

7.0

1 Evade (chlorothalonil) and Folicur CL are no longer marketed for use on peanuts.


Seed Rot and Seedling Disease

Seed rot and seedling disease of peanut are caused by soil-inhabiting fungi such as Aspergillus niger, Rhizoctonia solani and several species in the genus Pythium. Seed rot and seedling disease generally occur when soil conditions do not favor rapid seed germination and seedling growth. Typically, significant stand thinning is most likely to occur in peanuts planted in early to mid-April when the soil is cool and wet. Dry soil conditions will increase the incidence of post-emergence damping off due to A. niger. Poor seed quality will also contribute to the development of this disease. The frequency of cropping peanut may affect the severity of seed rot and seedling disease. Stand loss due to this disease is rarely severe enough to justify replanting.

Cultural Controls:

Sowing seed in a well-prepared seedbed with sufficient soil moisture for rapid seed germination and sustained seedling growth will minimize the risk of stand failures due to seed rot and seedling disease. In addition, delaying planting in April until soil temperatures at a depth of 4 inches reach 65 F will also help ensure rapid germination and growth. Peanut seed must be selected on the basis of a high rate of germination and good seedling vigor.

Cropping peanuts behind two or more years of corn, grain sorghum or a pasture grass may reduce the incidence of seed rot and seedling disease. Peanuts grown behind cotton should be planted when conditions favor rapid seed germination and seedling emergence.

Chemical Controls:

All peanut seed is treated with a machine-applied fungicide seed dressing prior to bagging. A small amount of seed is treated with the bacterial (Bacillus subtilis) inoculant Epic and Kodiak. No information was collected in the 1996 Peanut Producers Survey concerning the use of fungicide seed dressings for peanuts. The most commonly used fungicide seed dressings are listed below.

Gustafson 4-Way: captan + maneb + PCNB + etridiazole.

Vitavax PC: carboxin + PCNB + captan.

Prevail: carboxin + metalaxyl + PCNB.


Southern Stem Rot (White Mold)

In Alabama, southern stem rot is a common and often very destructive disease of peanut. Between 1991 and 1993, annual losses totaled nearly 20% of expected yield for an estimated $40 million income loss. Prior to the introduction of efficacious fungicides in the mid-90s, disease-related yield losses in selected fields exceeded 40% to 50% of anticipated peanut yields. Other common hosts of the causal fungus Sclerotium rolfsii are tomato, pepper, watermelon, soybean and beggarweed.

Southern stem rot severity is closely linked with the frequency of peanut production. In a 1991 to 1993 survey of Alabama peanut fields, the worst yield loss to this disease occurred when peanuts were cropped every year or in a one-year rotation with corn or cotton. When peanut followed two or more years of corn or cotton, stem rot-related crop injury was much lower and yields higher. The occurrence of southern stem rot in peanut cropped behind permanent pasture was extremely low. (19)

Southern stem rot is a hot, wet weather disease. Typically, colonization of host plants occurs primarily in July and August when day and night temperatures are above 90 F and 70 F, respectively. Good soil moisture levels also contribute to the onset and severity of this disease.

Cultural Controls:

Cultural practices, which can be used to reduce crop loss due to southern stem rot, include crop rotation, deep tillage and planting resistant cultivars.

Crop rotation is the most effective but underutilized weapon against southern stem rot. As mentioned above, loss to southern stem rot can be largely avoided by cropping peanut behind two years of a non-host crop such as corn, cotton, grain sorghum, summer forage grasses, permanent pasture or clean fallow. More frequent production of peanut usually results in significant disease pressure and unacceptable yield loss. However, sufficient tillable acres are not available in the peanut growing region to allow most Alabama peanut producers to implement a three-year rotation pattern.

Tillage practices such as turning land with a moldboard plow may help reduce disease pressure by burying the debris from the previous peanut crop as well as sclerotia (survival structures) of S. rolfsii. In fields where peanuts have been cropped for several consecutive years, an increase in southern stem rot damage has been seen in reduced or no-till peanuts as compared with those grown using conventional tillage practices. Burying the vines with soil when plowing peanuts for weed control will increase the severity of southern stem rot and directly reduce pod set around the taproot.

The peanut cultivars Southern Runner and FL MDR 98 are partially resistant to southern stem rot. Typically, these peanuts suffer 50% to 70% less damage than a susceptible cultivar. The cultivars Georgia Green and Andru 93 also appear to have some tolerance or resistance to this disease. Presently, Southern Runner, FL MDR 98 and Georgia Green account for 95% or more of the acreage planted to peanut in Alabama. (19)

Chemical Controls:

Approximately 60% to 70% of Alabama’s peanut acreage is treated with a fungicide for the control of southern stem rot. (5) Registered fungicides marketed for southern stem rot control include: 1) Folicur 3.6F (tebuconazole) at 7.2 fl. oz. per acre; 2) Abound 2SC (azoxystrobin) at 18 to 25 fl. oz. per acre; 3) Moncut 50W (flutolanil) at 2 lb. of product per acre; 4) Montero [twin pack containing Tilt (propiconazole) and Moncut 50W (flutolanil)]. For effective control, fungicide treatment programs are begun prior to the onset of southern stem rot symptoms. Depending on the fungicide chosen, from 1 to 4 applications are broadcast beginning the first week in July. Since Folicur 3.6F, Abound 2SC, Moncut 50W and Montero are all applied to the peanut foliage, a good rain or irrigation is needed to wash fungicide residues from the leaves down the stems and into the soil. Extended periods of dry weather will greatly reduce the effectiveness of these fungicides against southern stem rot. The products and total acres treated from the 1996 Statewide Peanut Producer Survey are listed in Table 2 below.

Tebuconazole is currently marketed on peanut as Folicur 3.6F at a rate of 7.2 fluid ounces per acre. The Folicur CL twin-pack of Folicur 3.6F and Bayer 720 (chlorothalonil) was only sold during the 1996 growing season. When a block of four successive sprays are applied every 10 to 14 days, this fungicide will give good control of both southern blight and Rhizoctonia limb rot. Typically, from 3 to 4 consecutive applications of Folicur 3.6F are applied at the beginning in late June or early July. According to the 1996 survey of Alabama peanut producers, an average of 3.1 and 4.0 applications of Folicur 3.6F and Folicur CL, respectively, were made to a total of 63.7% of Alabama peanut crop for the control of southern stem rot or Rhizoctonia limb rot. (5) Currently, Folicur 3.6F, which is widely used for the control of southern stem rot, also has excellent activity against peanut rust, southern stem rot and Rhizoctonia limb rot as well as some against CBR. For season-long control of leaf spot diseases and peanut rust, the block spray program for Folicur 3.6F is preceded and then followed by 2 applications and then a single application, respectively, of a chlorothalonil fungicide.

Azoxystrobin, which was released in 1997, is marketed as Abound 2SC. Two broadcast applications of Abound 2SC @ 18.5 to 24.6 fluid ounces per acre should be made approximately 60 and 90 days after planting for control of southern stem rot. For season-long leaf spot and rust control, apply the recommended rate of a chlorothalonil fungicide at 10- to 14-day intervals, before and after applying Abound 2SC. Abound 2SC also is recommended for the control of leaf spot diseases, peanut rust and Rhizoctonia limb rot.

Flutolanil was sold at the time of the 1996 survey as Bravo/Moncut Flowable. Application rate for this fungicide was 2.1 pints per acre and up to 5 applications could be made per season. Bravo/Moncut is, however, no longer being formulated. Currently, this fungicide is being marketed as Moncut 50W and in a twin pack with Tilt as Montero. Moncut 50W may be applied once at 2 pounds per acre or twice at 1 pound per acre. Montero application rates range from 1.5 to 1.85 pounds of product per acre. Depending on the rate used, 2 or 3 applications of Montero may be made to peanuts per growing season for the control of both Rhizoctonia limb rot and southern stem rot. Moncut 50W has no activity against leaf spot diseases and peanut rust and must be tank-mixed with either chlorothalonil or Tilt 3.6E.

Chlorpyrfos insecticide is marketed as Lorsban15G on peanut for the control of the lesser cornstalk borer, corn rootworm and wireworm on peanut. Since the early 1980s, this insecticide also has a label for the suppression of southern stem rot on peanut. Following the release of Folicur 3.6F, the use of Lorsban 15G for the suppression of southern stem rot drastically declined by 1996 to only 4.5% of Alabama peanut acreage. (5) Efficacy of Lorsban 15G is inferior to that of Folicur 3.6F, Abound 2SC and Moncut 50W (flutolanil). (8)

Table 2: Fungicides applied to peanut to control southern stem rot and/or Rhizoctonia limb rot, according to the Alabama 1996 Statewide Peanut Producer Survey

Fungicide and Rate/A

% Survey
Acres Treated

Avg. No. Sprays

Folicur 3.6F @ 7.2 fl. oz.

47.6

3.1

Folicur CL1

Bayer 720 @ 1 pt. +

Folicur 3.6F @ 4.1 fl. oz.

16.1

4.0

Bravo Moncut @ 2.1 pt.2

2.9

4.0

Lorsban 15G @ 13.3 lb.

4.5

1.0

1Folicur CL twin pack is no longer marketed in Alabama.
2Bravo/Moncut fungicide was withdrawn from market in 1999.

Typically, the fungicides in the table above will provide approximately 60% to 75% control of southern stem rot. Given favorable weather patterns (i.e., activating rainfall or irrigation), yield gains usually will range from 600 to 1,000 pounds of peanuts per acre. Decisions concerning fungicide use for a given field are largely made on the basis of cropping history and the producers’ recollection of disease problems in the past peanut crops. Due to the efficacy of available fungicides, scouting recently inverted peanut fields for stem rot damage is an ineffective method of scheduling fungicide treatments for the next peanut crop. Peanut growers are advised to check their fields in mid to late June to spot early outbreaks of southern stem rot. If active colonization of plants is seen, fungicide treatment programs should be initiated within the next few days. The combination of high spray program costs and low profit potential for peanuts may begin to reduce the size of the market for southern stem rot fungicides.


Rhizoctonia Limb Rot

Limb rot, which is caused by Rhizoctonia solani, is a damaging disease primarily on irrigated peanuts. Loss to this disease may also be seen in dryland peanuts with long, rank vine growth. Over watering, frequent showers, dense vine growth, over fertilization with nitrogen and tractor traffic will increase the disease severity and pod loss in peanut. Typically, limb rot development occurs during extended periods of hot, wet weather in August and early September. Since the majority of the pods shed due to limb rot are on the runners and the plants usually do not suffer heavy damage, yield loss due to this disease is not severe as compared with southern stem rot. (19)

Cultural Controls:

Unlike most other soilborne diseases of peanut, crop rotation appears to have little influence on the development of Rhizoctonia limb rot. Significant limb rot damage has been noted in peanuts grown behind a permanent bahiagrass pasture as well as fields in continuous peanut production.

Limiting vine growth may help reduce loss due to Rhizoctonia limb rot. Since the carryover of nitrogen from the previous crop will promote excess vine growth, corn and cotton produced prior to peanuts, particularly in irrigated fields, should be fertilized according to soil test recommendations. In highly fertile soils, sowing a peanut cultivar such as Georgia Green, which has a smaller vine and compact growth habit, is suggested. Cultivars that often produce rank vines, such as Southern Runner and FL MDR 98, are most likely to suffer some limb rot damage. An application of a soluble calcium source such as gypsum may help reduce pod loss due to Rhizoctonia limb rot, particularly on Virginia-type peanut cultivars.

Chemical Control:

Fungicides, when applied for the control of southern stem rot, will also control Rhizoctonia limb rot. Applications for limb rot alone are recommended in those fields with a history of significant disease-related loss or those with rank vines. See Table 2 for a listing of the acres treated and application number(s) for each fungicide. Lorsban 15G insecticide is not cleared for the control or suppression of Rhizoctonia limb rot and may in fact increase the severity of this disease on peanut.

Tebuconazole is currently marketed on peanut as Folicur 3.6F. Folicur CL was marketed for use on peanut in 1996 and then withdrawn. This fungicide must be applied every 10 to 14 days at 7.2 fluid ounces per acre for the control of Rhizoctonia limb rot. Typically, from 3 to 4 consecutive applications of Folicur 3.6F are applied at the beginning in late June or early July. According to the 1996 Peanut Producer Survey, producers made an average of 3.1 and 4.0 applications of Folicur 3.6F and Folicur CL, respectively, to their peanuts for the control of Rhizoctonia limb rot and southern stem rot. (5) Folicur 3.6F is also used not only for the control of leaf spot diseases and peanut rust, but also for the suppression of CBR. For season-long control of leaf spot diseases and peanut rust, the block spray program for Folicur 3.6F is preceded and then followed by 2 applications and then a single application, respectively, of a chlorothalonil fungicide.

Azoxystrobin, which was released in 1997, is marketed on peanut as Abound 2SC. Two broadcast applications of Abound 2SC at 18.5 to 24.6 fluid ounces per acre should be made approximately 60 and 90 days after planting for control of Rhizoctonia limb rot. For season-long leaf spot and rust control, apply the recommended rate of a chlorothalonil fungicide at 10- to 14-day intervals before and after applying Abound 2SC. Abound 2SC also is recommended for the control of leaf spot diseases, peanut rust and southern stem rot.

Flutolanil was sold at the time of the 1996 survey as Bravo/Moncut Flowable. Application rate for this fungicide was 2.1 pints per acre and up to 5 applications could be made per season. Bravo/Moncut is, however, no longer being formulated. Flutolanil is currently available under the trade names Moncut 50W and as a twin pack with Tilt 45W as Montero. Moncut 50W may be applied once at 2 pounds per acre or twice at 1 pound per acre. Montero application rates range from 1.5 to 1.85 pounds of product per acre. Depending on the rate used, 2 or 3 applications of Montero may be made to peanuts per growing season for the control of both Rhizoctonia limb rot and southern stem rot. Moncut 50W has no activity against leaf spot diseases and peanut rust and must be applied with a tank-mix partner such as chlorothalonil or Tilt. (8)

Abound 2SC has proven in some research trials to be slightly more effective in controlling Rhizoctonia limb rot than Folicur 3.6F or Moncut 50W. However, other studies indicate that the level of disease control provided by Abound 2SC and Folicur 3.6F was similar. The effectiveness of Montero for the control of this disease has not yet been determined.


Cylindrocladium Black Rot

In Alabama, Cylindrocladium black rot or CBR, which is caused by the soil fungus Cylindrocladium crotalariae, occurs most often in the three major peanut-producing counties bordering the Florida panhandle. Historically, this disease is most likely to occur in those fields where Virginia-type peanuts were grown in past years. High soil moisture levels, particularly in the late spring and early summer, favor the development of this disease. Symptoms of this disease are often confused with those of southern stem rot, peanut root-knot nematode and tomato spotted wilt virus. (17)

Cultural Controls:

In runner-type peanuts, few options for controlling CBR exist. Rotation to nonhost crops such as corn, cotton, grain sorghum and permanent pasture may be of some help. However, the survival structures (sclerotia) of the causal fungus remain viable in the soil for up to 20 years. Preliminary studies suggest that FL MDR 98 is less sensitive than most other runner-type cultivars to this disease. (17)

Chemical Controls:

The soil fumigants Vapam and Busan (metam sodium) are widely used in the Mid-Atlantic states on peanut pre-plant for the control of CBR. However, the occurrence of CBR is often too sporadic to justify such a costly treatment. According to the 1996 Peanut Producer Survey, none of Alabama’s peanut acreage was treated that year with either of these soil fumigants. See Table 4 for a breakdown of pre-plant fumigant use on peanut in Alabama.

Growers are advised to check each of their fields in August or September for symptoms of this disease and to note the location of "hot spots" on a field map for future reference.

Within the last two years, research in Georgia and North Carolina showed that Folicur 3.6F and Abound 2SC, when applied at the recommended 7.2 fluid ounces per acre and 18.4 to 25.4 fluid ounces per acre, respectively, suppressed CBR and significantly increased pod yield. In 1999, Folicur 3.6F (tebuconazole) was granted a 2ee label for the suppression of CBR on peanut. The application rate, treatment placement and timing are the same as that for the control of southern stem rot, Rhizoctonia limb rot, leaf spot diseases and peanut rust. (8)


Tomato Spotted Wilt Virus (TSWV)

The virus disease tomato spotted wilt, or TSWV, poses a significant threat to peanut production in Alabama and other states in the Southeast. In recent years, severe outbreaks along with sizable yield reductions have occurred in Texas and Georgia. So far, damage to Alabama's recent peanut crops has not been serious, but this disease is commonly found in every field of peanut in this state.

TSWV is transmitted to peanuts primarily by the tobacco and western flower thrips. The virus is acquired by the larvae feeding on diseased weeds or peanuts and is transmitted by the adults. Viruliferous adults may overwinter in the soil or survive on TSWV-infected winter weeds during the winter months. This virus is not seed transmitted. (15)

Cultural Controls:

All decisions concerning the control of TSWV are made prior to or at planting. The most critical factors involved in TSWV control in peanut are cultivar selection, seed quality, planting date and seeding rate.

Considerable differences in the resistance of peanut cultivars to TSWV have been observed. Generally, virus levels are 50% to 75% lower in the resistant than in the susceptible peanut cultivars. In 1996, the lone TSWV resistant cultivar Southern Runner ranked fourth (11.2% planted acres) in total acres planted (Table 3). Today, the remaining four cultivars are no longer widely planted in Alabama or in the other southeastern states. In 1999, the TSWV-resistant Georgia Green, FL MDR 98 and to a lesser extent Southern Runner, have been sown on nearly 100% of Alabama’s peanut acreage.

Planting date also has a considerable impact on the onset of TSWV in peanuts. Peanuts sown in early to mid-April are most vulnerable to TSWV. The combinations of erratic stand establishment and slow plant growth coupled with high populations of the thrips vector greatly increase the risk of TSWV infection in early-planted peanuts. The risk of disease gradually declines to its lowest point in early May and then begins to rise again by the middle to the end of the month. Planting seed with good germination and vigor at the correct seeding rate, all of which will ensure rapid stand establishment, are also effective strategies for managing TSWV in peanut. (15)

A sizable minority of Alabama peanut growers has recently modified their planters to allow for the production of Georgia Green peanuts on twin rows. Yield of twin row peanuts are often 10% to 15% higher than those of the same cultivar planted on traditional (36-inch) single rows. In addition, preliminary information indicates that the incidence of TSWV is lower in twin than in single row plantings of the same peanut cultivar. Twin row peanuts may, however, have more problems with other peanut diseases.

Table 3. Top peanut cultivars grown in 1996 and their reaction to TSWV

Peanut Cultivar

Reaction to
TSWV

Planted Acres
% of Total

Average Yield
Pounds/acre

Florunner

Susceptible

31.1

2,490

GK-7

Susceptible

28.0

2,671

Andru 93

Susceptible

13.5

3,022

Southern Runner

Resistant

11.2

2,595

Sun Runner

Susceptible

6.6

3,114

Chemical Controls:

Most insecticides applied at or post-plant have been shown to have little impact on the spread of TSWV in peanuts. Where TSWV pressure is likely to be very high, the insecticide Phorate (Thimet 20G) has been shown to reduce the numbers of virus-infected plants. Although the insecticide does provide good thrips control, suppression of virus infection is thought to be due to activation of the plants’ defenses by the slightly phytotoxic insecticide. (8)


Peanut Rust

Peanut rust, which is caused by Puccinia arachidis, occurs sporadically in Alabama but is quite destructive when left uncontrolled. This disease is rarely seen on peanuts in most areas of Alabama before early to mid-August. Peanut rust may, however, prove to be a serious disease on peanuts in new production areas in Baldwin and Mobile counties, both of which are close to the Gulf of Mexico. Extended periods of wet, cloudy weather favor the spread and development of peanut rust. (17)

Cultural Controls:

The cultivar Southern Runner has partial resistance to peanut rust. Some of the newly released peanut cultivars may also have some resistance to this disease.

Since the fungus disseminated from the tropics into Alabama on wind currents, practices such as crop rotation and tillage practices have little or no influence on disease development. (17)

Chemical Controls:

Although few fungicide applications are specifically made to control peanut rust, the standard and advisory spray programs are designed to prevent rust outbreaks in Alabama’s peanut crop. Peanut producers, particularly in those areas where rust outbreaks are most common, are advised to scout each field at weekly intervals beginning in mid-July for "hot spots" of peanut rust. If rust is found, the interval between fungicide sprays must be reduced to seven days. See Table 1 for a listing of foliar fungicides and their use pattern on peanut in 1996.

Chlorothalonil, which is marketed under the trade names Bravo 720 Weather Stik, Bravo Ultrex, Echo 720 and Terranil;, is the most widely used peanut rust and leaf spot control on peanuts. In 1996, approximately three to four applications of a chlorothalonil fungicide were made on 90% of Alabama’s peanut acreage. (5) Prior to the registration of Folicur 3.6F and Abound 2SC, up to 8 or more applications of a chlorothalonil fungicide were made per year for the control of peanut rust and leaf spot diseases of peanut. Efficacy of chlorothalonil fungicides against peanut rust and leaf spot diseases is quite good. If disease is severe, peanut producers are advised to shorten the spray interval from the recommended 10 to 14 days to as little as 7 days.

Tebuconazole is currently marketed on peanut as Folicur 3.6F. The Folicur CL twin pack of Folicur 3.6F and Bayer 720 was only sold during the 1996 growing season. When a block of four successive sprays are applied every 10 to 14 days, this fungicide will give good control of peanut rust and both leaf spot diseases. Typically, 3 to 4 successive applications of Folicur 3.6F are applied at the beginning of late June or early July at the interval listed above. According to the 1996 Peanut Producer Survey, producers made an average of 3.1 applications of Folicur 3.6F. Folicur 3.6F is also widely used not only for the control of peanut rust and leaf spot diseases but it is also effective against southern stem rot and Rhizoctonia limb rot. For season-long control of peanut rust and leaf spot diseases, the block spray program for Folicur 3.6F must be preceded and then followed by 2 applications and then a single application, respectively, of a chlorothalonil fungicide such as Bravo 720, Bravo Ultrex, Echo 720 or Terranil 6F.

Azoxystrobin, which was released in 1997, is marketed for use on peanuts as Abound 2SC. Two broadcast applications of Abound 2SC at 18.5 to 24.6 fluid ounces per acre, which should be made approximately 60 and 90 days after planting, are targeted mainly for the control of southern stem rot and Rhizoctonia limb rot. Abound 2SC, however, will also control peanut rust and both leaf spot diseases. For season-long leaf spot and rust control, apply the recommended rate of a chlorothalonil fungicide at 10- to 14-day intervals, before and after applying Abound 2SC.

Propiconazole (Tilt), which was also applied with a chlorothalonil tank-mix partner in late spring primarily for the control of early leaf spot, has little activity against peanut rust. Application interval for Tilt/chlorothalonil combinations is 10 to 14 days. For the 1996 growing season, 21.4% of Alabama’s peanut acreage was treated with this fungicide. (5, 8)



Nematodes

Root-knot Nematode

Peanut root-knot nematode (Meloidogyne arenaria) can severely limit the yield of peanuts and has proven to be difficult to manage. Yield loss is closely tied to cropping patterns: the more often peanuts are grown, the higher the risk of significant crop injury. Fields at highest risk are those cropped to peanut for three or more successive years. A 1980 survey showed that this nematode was present in 40% of Alabama’s peanut fields. Today, the percentage of fields infested with the root-knot nematode is probably higher.

Nematode injury is often difficult to diagnose. Damage to plants can easily be mistaken for the symptoms of a nutritional deficiency, a soil-related disorder, drought stress and soilborne diseases, such as southern stem rot or CBR. Often, the foliage looks normal while the roots and pods are badly galled. Symptoms of nematode injury never occur uniformly across a peanut field.

Unthrifty, stunted peanut plants are usually found in circular to irregular patches ranging from a few feet to several acres. During periods of hot, dry weather, severely damaged plants often die.

Due to the difficulty in identifying fields with moderate but damaging populations of the peanut root-knot nematode, collecting a soil sample for a nematode assay is recommended for any field going into peanuts the following year. According to the 1996 Survey of Alabama Peanut Producers, only 25.6% of respondents collected soil samples for a nematode assay. Records of the Plant Diagnostic Laboratory at Auburn University confirm that few peanut producers submit soil samples for a nematode assay and the above figure may be inflated. Often, harvesting operations interfere with sampling. Soil samples for a nematode assay often are not collected until late winter, which is after nematode populations reach their lowest levels of the year. As a result, false negative assay reports may be issued and critical nematicide treatments deleted. Typically, producers base their control decisions on assay reports from previous crops, historic cropping patterns or just an educated guess.

Cultural Controls:
Crop rotation will often prevent the buildup of peanut root-knot populations to damaging levels. Approximately 80% of peanut producers surveyed in the 1996 survey reported that they rotated peanuts with other crops, primarily corn and cotton. The best rotation for avoiding root-knot nematode entirely is growing one to two peanut crops behind four or more years of a pasturegrass (bahiagrass, bermudagrass and centipedegrass). Unfortunately, few growers have the land or economic resources to adopt such a cropping sequence. A minimum of 2 years between peanut crops is also an effective cropping pattern for nematode management. Cropping peanut behind 1 year of another crop, which is the most common rotation pattern followed by Alabama peanut producers, often promotes the buildup of root-knot populations to damaging levels. (5) The use of nematode-suppressive crops such as castor bean and velvetbean has also been proposed. However, the level of nematode suppression provided by these crops is similar to that provided by the nonhost crop cotton. In addition, seed of castor bean and velvetbean is quite expensive. Finally, nematode suppressive crops are practical only if they are a source of income or are of forage value (velvetbean). On a sizable portion of Alabama peanut acreage, continuous peanut production is a practice that eventually results in significant nematode-related yield loss.

As was the case in 1996, no root-knot resistant cultivars are in the commercial seed trade. Resistance has been bred into some peanut lines and resistant cultivars may be available within the next few years. The late maturing cultivar Southern Runner is more sensitive to root-knot nematode than other peanut cultivars and should not be planted in those fields where damaging populations are found. Planting an early maturing peanut cultivar such as Andru 93 along with using a recommended nematicide in root-knot nematode infested fields can help reduce nematode-related yield loss.

Peanut root-knot nematode survives on a number of broadleaf weeds, especially summer legumes. A good broadleaf weed control program in peanut and other rotation crops is essential for long-term nematode suppression. Heavy broadleaf weed pressure can offset the benefits gained from good rotation practices. Also, disking under volunteer peanuts is particularly important in fields in summer fallow or grass pastures.

No effective biological agents have been developed for the control of peanut root-knot nematode and none are on the horizon. (18)

Chemical Controls:
Nematicides can provide some protection from peanut root-knot nematode. Preferably, fields should be targeted for treatment with a nematicide on the results of a nematode soil assay or presence of damage on recent peanut crops. Of the producers surveyed, 31.9% applied a nematicide to their 1996 peanut crop. (5) Both fumigant and granular nematicides are registered for use on peanuts for the control of peanut root-knot nematode. Typically, the fumigant nematicides are applied approximately two to three weeks prior to planting with a moldboard plow while the granular products are applied on a narrow band, at- and in some cases, post-plant. By a wide margin (29.6% vs. 2.3% of acres planted), granular products are the most widely used nematicides on peanuts. (5) Typically, granular products are easier to apply and often provide better nematode suppression than fumigants. A listing of fumigant and granular nematicides and the percent of acres treated are listed in the table below.

Table 4. Fumigant and granular nematicides used and percentage of survey acres treated according to the Alabama 1996 Statewide Peanut Producer Survey

Pre-plant Fumigant Nematicides

% Survey

Acres Treated

At- and Post-plant Granular Nematicides

% Survey

Acres Treated

Busan

0

Nemacur 15G

0

Telone C-17

1.4

Temik 15G (T-band)

12.1

Telone II

<1

Temik 15G (In-furrow)

19.3

UCB

0

Temik 15G (Split At and Post-Plant)

4.3

Vapam

0

Mocap 15G

1.6

Metam-sodium is the active ingredient in Busan and Vapam. Neither product is currently marketed for use on peanut in Alabama (0% of survey acres treated in 1996).

Dichloropropene is a fumigant nematicide sold under the trade name of Telone II. When combined with 16.5% chloropicrin, this fumigant is marketed as Telone C-17 and may also be used to suppress selected soilborne diseases, primarily on vegetable crops. This product is usually far too costly to apply to peanuts. For light to moderate nematode infestations, apply Telone II pre-plant to peanuts at a 5 to 6 gallons per acre rate using a moldboard plow to a depth of 10 inches. In fields heavily infested with peanut root-knot nematode, broadcast rates of 9 to 12 gallons of Telone II per acre are required. Apply approximately 7 to 14 days before planting. In 1996, Telone II and Telone C-17 were applied to 2% of the surveyed acres. Questions concerning efficacy against the peanut root-knot nematode, a lack of application equipment and high product cost will continue to greatly limit the use of Telone II on peanut. When Telone II is used, an insecticide must be applied either in furrow, to the seed or as a seed dressing for thrips control.

Aldicarb (Temik 15G) may be applied on a narrow band at rates of 13.3 to 20 pounds of product per acre over the open seed furrow and lightly incorporated (12.1% of surveyed acres). An at-plant application of Temik 15G at 10 pounds per acre followed 40 days after planting by another 10 pounds per acre is also an option (4.3% of surveyed acres). Many producers view thrips control (Temik 15G applied at 6.7 pounds per acre) as a low-cost alternative to the higher rates (19.3% of surveyed acres). While this low rate will sometimes boost peanut yield, the higher rates have been shown to give superior yield gains. Research has shown that the yield gains obtained with rates from 10 to 20 pounds per acre rates of Temik 15G are similar. As a result, most peanut producers have been advised that there is no need to apply more than 13.3 pounds of Temik 15G (lowest rate for nematode control).

Fenamiphos (Nemacur 15G) may be applied at-plant at rates of 10 to 17 pounds of product per acre over the open seed furrow. Nemacur 15G is not used on peanuts due to poor activity against thrips and questions of product efficacy against peanut root-knot nematode (0% of surveyed acres treated).

Ethoprop (Mocap 15G) is registered for use at- or post-plant on peanut at rates of 20 pounds of product per acre as a banded treatment. Mocap 15G is not as efficacious as Temik 15G against peanut root-knot nematode and has no activity against thrips (1.6% of surveyed acres treated). (5, 8)



Contacts

  1. Program: Dr. Jesse LaPrade, Pesticide Impact Assessment Program Liaison for Alabama, Alabama Cooperative Extension System, Auburn University, jlaprade@acesag.auburn.edu, (334) 844-5533, Fax: (334) 844-9022.

  2. Insects: James R. Weeks, Extension Entomologist, Alabama Cooperative Extension System, Wiregrass Regional Research and Extension Center, Headland, jweeks@acesag.auburn.edu, (334) 693-2010, Fax: (334) 693-2957.

  3. Weeds: Dr. Glenn Wehtje, Professor Agronomy & Soils, Alabama Cooperative Extension System, Auburn University, gwehtje@acesag.auburn.edu, (334) 844-4100, Fax: (334) 844-3945.

  4. Diseases: Dr. Austin Hagan, Extension Plant Pathologist, Alabama Cooperative Extension System, Auburn University, ahagan@acesag.auburn.edu, (334) 844-5503, Fax: (334) 844-4072.

  5. IPM: Dr. Geoffrey Zehnder, Professor and IPM Coordinator, Department of Entomology, Alabama Cooperative Extension System, Auburn University, gzehnder@acesag.auburn.edu, (334) 844-6388, Fax: (334) 844-6391.

  6. Commodity Specialist: Dallas L. Hartzog, Extension Agronomist, Alabama Cooperative Extension System, Wiregrass Regional Research and Extension Center, Headland, dhartzog@acesag.auburn.edu, (334) 693-2010, Fax: (334) 693-2957.

  7. Ag Economist: Dr. Jerry Crews, Extension Ag Economist, Alabama Cooperative Extension System, Auburn University, jcrews@acesag.auburn.edu, (334) 844-3506, Fax: (334) 844-3519.

    References

    Online: NASS, Fact Finders for Agriculture, USDA, Alabama Agricultural Statistics Service, A Field Office of USDA's National Agricultural Statistics Service in cooperation with the Alabama Department of Agriculture and Industries:

    1. http://www.aces.edu/department/nass/bulletin/1996/pg05.htm

    2. http://www.aces.edu/department/nass/bulletin/1996/pg11.htm

    3. http://www.aces.edu/department/nass/bulletin/1996/pg18.htm

    4. http://www.aces.edu/department/nass/bulletin/1996/pg10.htm

    5. Alabama 1996 Statewide Peanut Producer Survey conducted by the Alabama Agricultural Statistics Service for the Alabama Pesticide Impact Assessment Program, Alabama Cooperative Extension System, Auburn University, Alabama. Available at the ACES website – http://www.aces.edu/department/crd/publications/TI-96-peanut.html
    6. 1998 IPM Alabama Program Report, published by AAES Division of Research Information, Auburn University, Alabama.

    7. IPM information from the NASS 1996 Statewide Peanut Producer Survey conducted by the Alabama Agricultural Statistics Service for the Alabama Pesticide Impact Assessment Program, Alabama Cooperative Extension System, Auburn University, Alabama.

    8. 99IPM-360, IPM for Peanuts, Insect, Disease, Nematode, and Weed Control Recommendations for 1999, Alabama Cooperative Extension System, Auburn University, Alabama.

    9. Circular 308, Biology and Management of the Lesser Cornstalk Borer in Peanut Fields, Alabama Agricultural Experiment Station, Auburn University, Alabama.

    10. ANR-598, Peanut Pest Management Scout Manual, R. Weeks, D. Hartzog, A. Hagan, J. French, J. Everest, T. Balch, Alabama Cooperative Extension System, Auburn University, Alabama. pp. 7-8.

    11. ANR-990, Sucking Pests of Peanuts in Alabama, July 1996, R. Weeks, Extension Entomologist, Associate Professor, Auburn University, Alabama.

    12. Jerry Crews et al 1996 Budgets for Major Row Crops in Alabama, Department of Agriculture Economics, AEC BUD 1-1, January 1996.

    13. ANR-500A, 1996 Alabama Pest Management Handbook, Volume 1, Alabama Cooperative Extension System, Auburn University, Alabama, pp. 133-159.

    14. ANR-752, Foliage Feeders On Alabama Peanuts, R. Weeks, Alabama Cooperative Extension System, Auburn University, Alabama.

    15. ANR-574, Tomato Spotted Wilt Virus on Peanuts, Revised April 1998, A. Hagan and R. Weeks, Alabama Cooperative Extension System, Auburn University, Alabama.

    16. ANR-856, Nematode Suppressive Crops, Revised Feb. 1998, A. Hagan, W. Gazaway and E. Sikora, Alabama Cooperative Extension System, Plant Pathology, Auburn University, Alabama.

    17. ANR-369, Foliar Diseases of Peanuts, Revised Sept. 1998, A. Hagan, Alabama Cooperative Extension System, Plant Pathology, Auburn University, Alabama.

    18. ANR-393, Nematode Pests of Peanut, A. Hagan, Alabama Cooperative Extension System, Auburn University, Alabama.

    19. ANR-368, Soilborne Diseases of Peanut, A. Hagan, Alabama Cooperative Extension System, Auburn University, Alabama.


    Database and web development by the NSF Center for Integrated Pest Managment located at North Carolina State University. All materials may be used freely with credit to the USDA.