Crop Profile for Pecans in Louisiana
Prepared: April, 2005
Louisiana harvested 17.7 million pounds of pecans in 2003. This is 2.1 million pounds above the five-year average of 15.6 million pounds. This was composed of 8.1 million pounds of improved pecans and 9.6 million pounds of native pecans. The gross farm value was estimated at $15,068,567, which is 3.6 times the 2002 gross farm value. The 2002 pecan crop final USDA estimate for Louisiana was 6 million pounds. The 2002 crop was in a cyclic down crop year. Also, trees had severe storm damage and nuts had very low prices to further reduce the crop yield. The 2003 pecan crop was in a cyclic up year and had excellent growing conditions all season in most areas and good harvesting weather. The size of the crop was further enhanced by excellent prices that encouraged growers to be more thorough in their harvesting. The good prices also encouraged a large harvest from yard trees.
Production Methods:
Pecans are produced from native (seedling trees) or from orchards of improved (clonally-propagated) varieties. Most pecans produced in Louisiana come from native groves that have been improved and are managed with few inputs. Improvement of native groves generally involves removal of competing trees and shrubs; thinning of pecan trees to retain trees with highest production, best nut quality and highest disease resistance; establishment of permanent ground cover under trees (grasses and legumes) and fertilization.
Native pecan acreage is often grazed by cattle and this presents challenges for the use of pesticides. Most acreage of native pecans is harvested mechanically.
Improved pecan varieties are grown in orchards with management to control diseases, insect pests, and weeds. Drip irrigation is used in rare cases. Improved pecan orchards are harvested mechanically. Yield is higher and more consistent per tree for improved varieties and nut quality is higher. However, production inputs and management intensity are also higher for improved varieties as compared to native varieties.
Commodity Destination(s):
Pecans are sold in-shell through local retail outlets and to pecan processors who sell shelled pecans through various market channels. The distribution of Louisiana pecan production between these methods of marketing is unknown.
Worker Activities:
Pruning of pecan trees is performed in the dormant season. Occasional pruned falling limbs can cause slight injuries.
Post-emergence herbicide applications are made in early summer and occasionally after harvest primarily with tractor mounted sprayers although backpack sprayers are occasionally used. Row-middles are mowed or grazed during the growing season.
Insecticides and fungicides are applied from early spring up to harvest primarily with orchard blast sprayers to 75-80% of the improved acreage and approximately 30% of the native acreage.
Mechanical tree shakers followed by a mechanical ground harvester are utilized by a majority of growers. Occasionally, falling limbs due to the mechanical shaker causes slight injuries.
Note:
All pest control measures and pesticides mentioned in this profile reflect the current trends of Louisiana growers.
Pecan Nut Casebearer
Acrobasis nuxvorella
This gray moth is nocturnal and the most damaging insect pests of pecan in Arkansas. Eggs are laid on the tip end of the nutlets. Females will lay 50-150 eggs during their 5-8 day life span. The eggs are white when laid, but turn pink to red prior to hatching. These eggs will hatch in 4-5 days. The green caterpillars grow up to 13mm in length and feed in the developing nuts. Silk webbing with conspicuous dark colored frass eliminated by the larvae is usually seen holding the infested nuts together at their base. Even one larvae is capable of destroying all the nuts in a cluster. Warm spring temperatures influence Casebearer development. Cool, rainy weather can delay moth activity and egg laying. The period of egg laying can vary as much as two weeks from year to year. The second-generation larvae also attack the nuts but the damage is less severe. Later generations feed on the foliage or in the green shuck, causing very little damage. These insects have from one to four generations per year. By carefully monitoring egg hatch and with good control of the first and second generation, the third and fourth generations will be controlled. The first generation is the most damaging.
Control: Scout for eggs and larvae when the tips of the nuts turn brown after pollination, inspecting 200 nut clusters. Insecticide control should be applied 2-3 days after the first eggs hatch or when you find 1-3% nut cluster damage. See section on insecticides.
Hickory Shuckworm
Cydia caryana or Laspeyresia caryana
These are brown-headed, dirty white caterpillars. They can be up to 13mm long as mature larva. They feed internally in the immature nuts and cause them to drop. After shell hardening they feed inside the green shucks which prevents proper kernel development.
This insect is most active at night, and overwinters as a larva in the shucks of nuts. It begins attacking nuts in early-June and continues until harvest. In newly dropped nuts, you can often detect a chalky, white deposit at the larval entry point. This deposit is the scales of the female moth, placed to protect and seal the egg to the shuck. The larva will create a paper thin "window" in the shuck prior to pupation, which protects the pupa and provides an easily torn exit hole. Shuckworms have 3-4 generations per year. Emergence of the shuckworm varies from year to year and orchard to orchard depending on the temperature. The adult moths are dark-gray with a one-half inch wingspan.
Control: Activity should be monitored with use of two black-light traps per orchard. Check the light traps three times a week looking for adult moths. In the absence of black-light traps, start scouting for activity in July using pheromone traps. See section on insecticides.
Pecan Phylloxeras Complex:
Pecan Phylloxera Phylloxera devastatrix Pergande
Pecan Leaf Phylloxera Phylloxera russelae Pergande
Phylloxera notabilis Pergande
There are several species of phylloxera that attack pecan, and this appears to be a pest on the rise in Louisiana pecan production. These are very tiny greenish-yellow aphid-like insects contained in galls, abnormal swellings, on the leaves or stems. Stem infestations can weaken the shoots that will cause shoot death. Leaf infestations are not severe or damaging to a mature tree but can contribute to premature defoliation. Phylloxera produce galls where nut clusters would normally develop. They overwinter in the egg stage in protected places on the tree. There are several generations per year as long as there is new growth on the tree.
Control: Inspect pecan trees for phylloxera in May. Mark the trees that have galls on them for treatment the following year. Dormant oil may be applied to trees before bud break in late-February to early-March. Insecticides may be applied after eggs hatch in the spring but before nymphs are protected inside the galls. This is usually after bud break when leaves are 1-2 inches long. See section on insecticides.
Pecan Leaf Scorch Mite
Eotetranychus hicoriae McGregor
These mites are about 0.2 mm in size. They are long and pale green in color. They feed primarily along the midribs and veins on the underside of the leaves. This feeding causes a scorch appearance on the foliage. Infestations usually begin in the lower portions of the tree and move upward. In some instances, almost complete defoliation will occur. Damage occurs in June through September and appears as dark brown blotches on the leaflets. These mites overwinter in bark crevices on the tree limbs. Their life cycle is usually 11-15 days.
Control: See section on insecticides.
Pecan Weevil
Curculio caryae Horn
Adults of the pecan weevil are a brownish-gray in color and about 13 mm in size. They attack pecans and hickory prior to shell hardening causing the nuts to drop. Nuts in the water stage, if fed on by this weevil, will drop prematurely. Damaged nuts usually have a pinhole puncture surrounded by a dark moist stain. After the water stage, but during the jell stage, females chew a hole through the shell and deposit eggs inside the nut. Larvae hatch and feed in the nut for several weeks destroying the kernels. Mature larva have a brown head, are creamy white, and legless. They leave the nut to drop down and pupate in the soil. A complete life cycle requires 2-3 years.
Control: See section on insecticides.
Nut Curculio
Conotrachelus nicoriae (Schoof)
The dark gray to reddish-brown adults of the nut curculio are 5 mm long. They have a slightly curved snout that is approximately one third their body lengths. The larvae are small, legless creamy white grubs and are found inside the nut. Adults attack the immature nut with their snouts. Females make shallow crescent shaped punctures with their snout then deposit an egg. Eggs hatch within 4-5 days. These adult punctures are very visible and cause sap bleeding that resembles a tobacco stain. This feeding will cause premature nut drop. Adults overwinter in the ground trash and other protected places. This is an occasional minor pest. There is one generation per year.
Control: There is no currently registered insecticide for this pest. However, it appears to be controlled in a secondary manner by insecticide sprays for other insect pests.
Yellow Aphids Complex:
Black-Margined Aphid Monellia caryella
Yellow Pecan Aphid Monelliopsis pecanis
Both the yellow pecan aphid and black-margined aphid are similar in appearance and cause similar types of damage. These aphids are very small (1.5mm) and green-yellow in color. Yellow pecan aphids have red eyes and long setae that tend to stand out from the body at 45 to nearly 90-degree angles giving them a pincushion look. The black margined-aphid has much shorter setae that are less than a 45-degree angle with the body. Both species have multiple generations per year. They both feed on the under surface of the leaves. The yellow hickory aphids feed on the network of small veins located throughout the leaf while the black-margined aphids feed on the underside of leaves on the major leaflet veins. They secrete honeydew which promotes black sooty mold growth. Both the honeydew and mold coating the leaf surface will interfere with photosynthesis efficiency. Fire ants have been known to protect these aphids from their natural enemies.
Control: Separate chemical control is not usually recommended as this pest is controlled by treating other pests.
Black Pecan Aphid
Melanocallis caryaefoliae
Black pecan aphids are dark-green to black-green in color. They are very small and about 1.2 mm in length. They feed on top and bottom surfaces of the leaflets causing bright yellow areas that later turn brown and die. These aphids can be serious pests of pecan. They cause premature leaf drop and contribute to defoliation of the tree.
Control: See section on insecticides.
Predominant insecticides used in current Louisiana pecan production:
Lorsban 4E (chlorpyrifos) at 1.5 to 2.0 qt/A for pecan phylloxera, pecan nut casebearer, and Hickory shuckworm. REI: 24 hr. PHI: 28 days
Confirm 2F (tebufenozide) at 8 to 16 oz/A for pecan nut casebearer and Hickory shuckworm. REI: 4 hr. PHI: 14 days
Kelthane MF (dicofol) at 1 pt/A for pecan leaf scorch mite. REI: 12 hr. PHI: 7 days
Provado 1.6F (imidacloprid) at 3.5 to 7.0 oz/A for pecan phylloxera and all aphids. REI: 12 hr. PHI: 14 days
Warrior (lamda-cyhalothrin) at 2.56 to 5.12 oz/A for pecan phylloxera, pecan nut casebearer, Hickory Shuckworm, pecan weevil, and all aphids. REI: 24 hr. PHI: 14 days
Mustang Max at 2.56 to 4 oz/A for pecan phylloxera, pecan nut casebearer, pecan weevil, and all aphids. REI: 12 hr. PHI: 21 days
*Of the Louisiana pecan producers who do spray for insects, approximately 85% of all applications contain at least one of the above mentioned insecticides.
Management of weeds in native pecan groves consists of mowing the permanent ground cover and/or grazing by livestock. Weed control in pecan orchards with improved varieties is more intensive and is required for attainment of maximum yield. Weeds interfere with pecan production by competing for moisture and nutrients, producing chemicals that inhibit tree growth (allelopathy), and decreasing mechanical harvesting efficiency. The most commonly used system of orchard weed control is a herbicide strip in the tree row with mowed sod row middles. Maintenance of row middles in sod improves orchard access during wet conditions and mowing reduces competition with the trees. Cultivation is generally not practiced due to concerns about erosion and reduced tree health and growth.
Post-emergence herbicides used to maintain the strip
Glyphosate
Paraquat
Scant statistics exist on the percentages of acreage sprayed with post-emergence herbicides. However, a greater percentage of growers of improved varieties implement weed control with herbicides alone or in combination with livestock grazing. Approximately 60% of those who use chemicals for postemergence weed control use a glyphosate product.
Pecan Scab
Fusicladosporium effusum (Winter) Partridge & Morgan-Jones
Pecan scab is the most economically important disease of pecan in Louisiana. In commercial pecan orchards it annually causes lower yields and increased management costs. The fungus that causes pecan scab can infect growing stems, leaves, and nut shucks. The pinpoint to quarter-inch diameter lesions are light brown to black. Lesions can coalesce to produce larger areas of dead tissue that can kill stems, cause defoliation, and destroy nut development. Severe early infection of nuts can result in complete crop loss. Less severe infections and infections that occur later in the season reduce the growth of nuts which lowers yields. The severity of scab is influenced by rainfall frequency in spring and summer and by cultivar susceptibility to infection by the pathogen. Rainfall creates conditions that result in infection periods when the pathogen is present. Cultivar susceptibility varies widely from extremely susceptible to infrequent infection. However, the pathogen has often developed new races and most cultivars that were once not easily infected are now considered susceptible. Because of the often transient nature of cultivar resistance, commercial pecan growers in the southeastern U.S. are dependent on fungicides for control of pecan scab.
Control: The application of fungicides before infection occurs is the most effective way to control this disease. See section on fungicides.
Shuck Dieback/Decline (unidentified cause)
Anthracnose/Stem End Blight (Glomerella cingulata)
The etiology and epidemiology of shuck dieback and anthracnose are not well understood. They are believed to have separate causes but are often grouped together because they occur at the same time, have similar appearances, and may even occur on the same nut. Both problems become visible in August and/or September as nuts approach maturity. Shuck dieback is the more prevalent of the two phenomena and is thought to be related to stresses on the trees such as excessive crop, inadequate sunlight, and nutritional stress. In the majority of instances, shuck dieback first becomes visible at the distal end of the shuck as the shuck begins to die and turn black. This necrosis progresses towards the base of the nut and the shuck may flare open producing a tulip-like appearance or the shuck may stick tightly to the nut. Nuts with shuck dieback often remain attached to the terminal until typical nut maturity. The kernels of affected nuts will vary in degree of filling from well-filled, good quality nuts to useless wafers depending on the degree of kernel filling that had developed when shuck dieback started.
Control: There is no recommended control method for shuck dieback; however, research suggests that it may be possible to reduce the level of shuck dieback by thinning the nut crop during the liquid endosperm stage with mechanical shaking.
Anthracnose is caused by a fungal infection of the nut shuck. Most often the visible symptom of shuck necrosis begins near the base of the nut and is often referred to as stem-end blight. The disease becomes visible in late summer and early fall. Nuts affected with anthracnose usually abscise shortly after the onset of shuck necrosis. Kernels of infected nuts are generally of poor quality. Anthracnose appears to be less common than shuck dieback.
Control: Some fungicides applied full-season have significantly reduced the incidence of anthracnose. However, because the disease tends to be sporadic in its occurrence, recommendations for control of this disease are generally not made.
Vein Spot
Gnomonia nerviseda Cole
Vein spot is a common foliar disease on pecan in Louisiana. Spores of the fungal pathogen are produced in leaf debris from the previous year’s disease. Infection of the current season foliage usually develops following spring rainfalls. If there is less rainfall in the spring months than normal, infection may occur following rainfall in the summer period. Lesions begin to appear in late May. Lesions of vein spot disease always occur on vascular associated tissues including leaflet veins, midribs, petiolules, and rachises. The lesions are similar in size to scab lesions, but have a smooth surface and become gray in the center as they age. Vein spot disease can cause defoliation during late summer and fall. Infection and defoliation vary with cultivar; some cultivars have been recorded with a defoliation of over 70%.
Control: Vein spot can be controlled by fungicide applications during spring and early summer. See section on fungicides.
Pecan Bacterial Leaf Scorch
Xylella fastidiosa
Bacterial leaf scorch occurs on many cultivars in Louisiana. Symptoms usually begin in mid-summer; leaflets turn brown beginning at the tip and outer margins and leaflets abscise soon after they begin to turn brown. Symptoms may occur throughout a tree or be only on a few of the scaffold limbs. Defoliation of over 60% has been recorded on trees with severe symptoms. Infections are chronic and the disease is usually present every year to some extent. The disease can cause large economic loss over the lifetime of infected trees. It is not known how the pathogen infects trees in nature, but it is suspected that it is transmitted by xylem-feeding insects, such as leafhoppers, because that is the typical method of pathogen spread in other hosts. The pathogen can be transmitted through pecan scion wood and this may be a significant source of infection because pecan cultivars are clonally propagated. It is not known how the environment affects disease development.
Control: There is currently no way to “cure” trees of the disease once infection has occurred. Because the pathogen can be graft-transmitted, efforts should be made to collect scion wood only from trees that do not develop leaf scorch during the summer months.
Pecan Bunch Disease
A Phytoplasma
This disease causes shortened internodes that produce a “witches-broom” appearance on affected limbs. Terminals affected by bunch disease produce crowded shoots from numerous buds that normally would not be active. These dense, compact shoots often look like a broom head sticking out of a limb. Terminals with bunch disease usually start growing earlier in the spring than the unaffected terminals. This premature shoot growth provides an easy way to identify the disease in the spring. Terminals with bunch disease can be more difficult to recognize after trees are in full foliage. The disease may occur throughout a tree or be limited to a few scaffold limbs. Movement of the disease within a tree and between trees can occur slowly over a period of many years or be fairly quick spreading throughout an orchard in three to four years. It is not known how the pathogen infects trees but it is suspected that insect vectors are involved because leafhopper vectors transmit phytoplasm pathogens in other plant diseases. Often, the disease appears to move into a grafted orchard from seedling trees in wooded areas near the orchard. The pathogen also can be graft-transmitted. Terminals with the disease do not produce nuts, and thus a significant level of the disease can cause economic yield loss. Terminals that are not affected by the disease can produce good quality nuts.
Control: No effective method of control is known for this disease. Removing limbs with symptoms or entire trees will sometimes slow the spread of the disease within an orchard, but it usually does not eliminate it and symptoms will reoccur over time. Care should be taken to avoid collecting scion wood from infected trees. Some cultivars are apparently more resistant to infection than others. Consult with pecan specialists before selecting cultivars for planting if bunch disease is prevalent in the seedling population of your area.
Downy Spot Disease
Mycosphaerella caryigena Demaree and Cole
The fungus that causes downy spot forms light yellow, circular spots on the underside of leaflets in the spring. As the spots become older, they turn yellowish-brown and are visible on both surfaces of infected leaflets. Leaflets with numerous spots will defoliate in early summer, which reduces the vigor and productive capacity of trees. In Louisiana, the disease is sporadic and is most common on cultivar Stuart trees growing in low lying, humid areas and along waterways.
Control: Orchards that are regularly treated with fungicide for control of pecan scab on the foliage usually do not have a significant problem with downy spot. Whenever downy spot has been a significant problem, it was brought under control by early season application of fungicides. See section on fungicides.
Powdery Mildew
Microsphaera penicillata (Walr.: Fr) Lév
The fungus that causes powdery mildew can infect both leaves and nuts but under typical orchard conditions it is observed much more frequently on nuts. The fungus is first visible on nuts as a white powdery coating. As the nuts age, the white fungal growth disappears, but the nut shuck develops a brownish patina instead of the typical bright green. Generally, powdery mildew does not cause significant crop damage, but it can reduce nut quality in severe infections. The disease is sometimes a problem on pecan foliage in greenhouses and nurseries.
Control: In most instances, specific fungicide applications for control of powdery mildew in orchards are not necessary. Some of the fungicides labeled for pecan scab control also are effective in reducing the level of powdery mildew.
Predominant fungicides used in current Louisiana pecan production:
The following are sprayed for Pecan scab, Vein spot, and Downy spot.
Super Tin 80WP (triphenyltin hydroxide) at 7.5 oz/A REI: 48 hr. PHI: 30 days
Enable 2F (fenbuconazole) at 8 oz/A REI: 12 hr. PHI: 28 days
Orbit 3.6E (propiconazole) at 6-8 oz/A REI: 48 hr. PHI: 30 days
Syllit 65 WP (dodine) at 2 lb/A REI: 48 hr. PHI: 14 days
Sovran 50WG (kresoxim-methyl) at 3.2 oz/A REI: 12 hr. PHI: 45 days
Stratego (propiconazole + trifloxystrobin) at 10 oz/A REI: 24 hr. PHI: 30 days
*Of the Louisiana pecan producers who do spray for diseases, approximately 70% of all applications contain either Super Tin 80WP, Orbit 3.6E or Enable 2F.
This document was prepared by Matt Shipp.
Michael Hall, Ph.D.
LSU AgCenter
Pecan Research-Extension Station
P.O. Box 5519
Shreveport, LA 71135-5519
Phone: 318-797-8034
Fax: 318-676-7371
mhall@agctr.lsu.edu
Randy Sanderlin, Ph.D.
LSU AgCenter
Pecan Research - Extension Station
P.O. Box 5519
Shreveport, LA 71135-5519
Phone: 318-797-8034
Fax: 318-676-7371
rsanderlin@agctr.lsu.edu
John Pyzner, Ph.D
LSU AgCenter
Pecan Research-Extension Station
P.O. Box 5519
Shreveport, LA 71135-5519
Phone: 318-797-8034
Fax: 318-676-7371
jpyzner@agctr.lsu.edu
Mary Grodner, Ph.D.
Department of Entomology
LSU AgCenter
404 Life Sciences Building
Baton Rouge, LA 70803
225-578-2180
mgrodner@agcenter.lsu.edu
Charles Graham, Ph.D.
LSU AgCenter
Pecan Research - Extension Station
P.O. Box 5519
Shreveport, LA 71135-5519
Phone: 318-797-8034
Fax: 318-676-7371
cjgraham@agctr.lsu.edu