Crop Profile for Pecans in Georgia

Prepared: August, 2001

 

General Production Information

PRODUCTION

WORKER EXPOSURE ISSUES

 

 

Insect Pests

Insects attack both the foliage and nuts of pecans. Nut damage reduces yields and may make nuts unacceptable. Foliage injury reduces yields and nut quality.

Regular scouting is the foundation of pecan IPM. Each week, scouts examine foliage and nut clusters on 10 terminals per tree for insect pests, diseases, or damage. Approximately 10% of the trees are sampled each week. Additionally, growers use survey traps and knockdown sprays to monitor populations of hickory shuckworm and pecan weevil.

For more detail about pecan insect pests, visit http://www.gaipm.org/id/pecansi.html

Foliage pests

The black pecan aphid and yellow aphids (two species) are very serious pests of pecan. Aphid feeding removes water and plant nutrients from the trees. Aphids also excrete a sugary liquid called honeydew. Sooty mold fungus grows on honeydew and block sunlight from the leaf surface. Additionally, the black pecan aphid injects a toxin that produces a discolored spot on the leaflet; the leaflet will often drop as a result of the damage. Severe outbreaks of black pecan aphid cause defoliation of the tree.

The black pecan aphid is a very serious pest. Prior to July 1, growers apply pesticide if 25% of the scouted leaves have two more black pecan aphids. After July 1, pesticide is applied if 15% of the scouted leaves have two or more black pecan aphids or honeydew is rated ‘heavy’.

During the early season, growers do not apply pesticide if yellow aphids are the only insect pests. Yellow aphid infestation is less damaging early, and insects/disease help control aphid populations. After July 1, a pesticide is applied if the scout reports an average of more than 20 yellow aphids per compound leaf.

Systemic pesticides and foliar pesticides are commonly used to control aphids in pecans. Aldicarb and imidacloprid are systemic insecticides recommended for both yellow and black aphids. Foliar insecticides recommended for both yellow and black aphids include pyrethroids (esfenvalerate, cypermethrin, and zeta-cypermethrin), organophosphates (chlorpyrifos and disulfoton), an organochlorine (endosulfan), and imidacloprid.

For black pecan aphid, dimethoate, phosmet, and methidiathion are also recommended.

Insecticide resistance is a primary concern in aphid control. Where pyrethroids have been used extensively, growers must often apply mixtures of a pyrethroid and an organophosphate. Extension specialists recommend that pyrethroids should not be used (alone or in combinations) for early or mid-season applications. An organophosphate may also be added to an application of imidacloprid to manage resistance and provide better control of black pecan aphid. Finally, growers are urged not to apply imidacloprid as a foliar application to any orchard that received a soil application of imidacloprid.

Fire ants are known to protect aphids from their natural predators. Fire ants should be controlled or at least kept out of pecan trees. Chlorpyifos is recommended as a ground or trunk spray.

Mites, primarily the pecan leaf scorch mite, can cause defoliation. Generally, mites are a late season pest. Damaged leaves appear brown or scorched. Infestations often begin in lower limbs and spread rapidly up and out. Dicofol and fenbutatin-oxide are recommended for mite control.

Phylloxera and spittlebugs may also require treatment in some orchards. The pecan phylloxera is a small, aphid-like insect that is rarely seen, but the galls it produces are prominent and easily noticed. Severe infestations cause malformed, weakened shoots that finally die; such infestations can destroy entire limbs.

The spittlebug nymph sucks juices from the buds, young shoots, and nut clusters of the pecan tree. Heavy feeding by these insects may kill terminal shoots and/or reduce nut size, resulting in a smaller crop.

Endosulfan and chlorpyrifos are recommended to control both pests. Azinphos-methyl and imidacloprid are also recommended for spittlebug control.

Nut pests

Pecan nut casebearer can be an important pest because the larvae feed directly on the nuts. In normal years, light infestations do not require control. The most serious damage occurs in mid May. Monitor for adult emergence by placing pheromone traps in orchards by mid April. Begin scouting for nut casebearer in the first week of May, with particular attention to orchards not under a spray program in the previous year and to orchards with a history of nut casebearer infestation. Pesticide application is recommended when 3% of the nut clusters have eggs or damage. Time sprays to prevent infestation of more than one nut per cluster. If infestations are heavy, make a second pesticide application in one week. On rare occasions, additional pesticide applications may be necessary to control second generation emergence in mid June.

Although pyrethroids are registered for this use, they should not be used to control first generation nut casebearer to avoid aphid exposure to these chemicals (threat of resistance) and to preserve beneficial populations.

Pecan Weevil is most damaging late in the season. Adults emerge from July to October. Emergence should be monitored with traps and/or knockdown sprays. Monitoring should focus on trees with a recent history of weevil problems.

The pecan weevil causes two types of damage to the nut crop. First, the adult weevil punctures while feeding, and the immature nuts often fall. This damage is not easy to recognize and may be confused with damage from sucking bugs (e.g., stink bugs/plant bugs) or the hickory shuckworm. Another type of damage occurs when the female weevil deposits eggs in the nuts after the kernels form. The hatching larvae then devour the interior of the nut. This damage is most noticeable at harvest time by the lightness of the nuts or by the prominent exit hole where the grub has escaped.

If excessive nut drop results from adult feeding punctures before pecan shells harden, spray immediately. After shells harden and nuts reach ‘dough’ stage, apply pesticide when weevils emerge (especially following rains) and continue at 7-10 day intervals until weevil emergence stops. Carbaryl is the recommended pesticide, but carbaryl may cause buildup of damaging mite or aphid populations. If black aphids are present, growers are advised to add an organophosphate insecticide to the carbaryl spray.

Pyrethroids, phosmet, and methyl parathion are also registered for control of pecan weevil. However, they are not recommended to control heavy infestations. These materials may be adequate to prevent adult feeding injury prior to shell hardening.

Hickory Shuckworm are active throughout the season but do not cause significant damage until June or later. Prior to shell hardening, infestations cause nuts to drop. After shell hardening, the larvae tunnel into shucks, disrupting nutrient flow. As a result, the nuts stick to shucks, fail to fill, and reduce yields.

Black light traps monitor adult emergence and often capture many adults. The traps should be operated at least three nights/week. Pesticides are recommended when 7 or more moths are caught in a single trap or four moths are caught in a single trap for three consecutive nights.

Pheromone traps are also available; follow the directions provided with the traps. In orchards with a history of infestation, pesticide may be necessary in early June. Beginning at ½ shell hardening in August, 2-3 additional sprays should be applied at two-week intervals.

Combinations of pyrethroids (esfenvalerate, cypermethrin, or zeta-cypermethrin) and chlorpyrifos, phosmet, methyl parathion, or tebufenozide are recommended.

Kernel feeding hemipterans (stink bugs and plant bugs) may be present in the orchard all year, but they typically do not cause significant damage until late August-September. Their feeding causes nuts to drop prior to shell hardening. After shells harden, their feeding reduces nut quality by causing black, bitter spots on the kernels.

Scouting reports should report stink bug/plant bug numbers throughout the season; special attention should be given during the late season. If knockdown sprays are used to monitor pecan weevil, stink bugs/plant bugs should also be counted. Stink bugs/plant bugs may build up on other crops or weeds and then migrate to pecans to suck sap from developing nuts. Weed control in and around orchards helps reduce populations.

Pesticides are recommended when one stink bug/plant bug is reported per 40 terminals or when five or more bugs are found per knockdown spray on a sheet covering 20% of the area under the tree.

Proper timing of pesticide spray is difficult, so no insecticides provide consistent control. Methyl parathion, zeta-cypermethrin, and phosmet have provided satisfactory control.

 

Insecticides used on Georgia pecans (USDA Agricultural Chemical Usage, Fruit & Nut Summary, 1999)

Insecticide

Percent crop treated

# applications

Rate/application lbs/acre

Rate/crop year lbs/acre

chlorpyrifos

52

2.5

0.94

2.42

cypermethrin

18

1.9

0.08

0.16

dimethoate

48

2.2

0.29

0.65

endosulfan

5

1.8

0.75

1.36

imidacloprid

33

2.2

0.04

0.09

lindane

24

1.2

0.39

0.47

phosmet

8

1.0

1.25

1.25

note: [lindane is no longer available]

 

 

Diseases

Without regular pesticide applications, it would not be possible to produce a profitable pecan crop in Georgia. Scouting reports can help spray timing, but most diseases can only be controlled with protective applications of pesticides. As a result, growers apply pesticides on a calendar schedule to control pecan diseases. The timing of the spray program is based on the tree phenology, weather forecasts, and scouting information.

AU-PECAN. A newly developed program ‘AU-Pecan’ was developed at the University of Georgia to base fungicide applications on the occurrence of heavy fog or the likelihood of rain within five days. It has been proven successful, and the program reduces the number of fungicide applications by an average of 2+ per season.

HOW TO USE AU-PECAN, A WEATHER-BASED SYSTEM FOR CONTROLLING PECAN SCAB

Paul Bertrand Tim Brenneman Department of Plant Pathology The University of Georgia

  1. EQUIPMENT 1. Plastic rain gauge that will measure 0.1" of rain located in each orchard. 2. Access to a weather forecast giving % chance of rain each of the next five days. This is available on some TV weather forecasts or on the internet. The internet weather forecast is at www.awis.com. Look for AU-PECAN or use AU-PNUT. The table that comes up will give the % chance of rain for each of the next five days and a 5-Day Average for several SouthEast regions. Use column headed 5-Day Average as the AU-PECAN rain forecast.
  2. SETTING A PROTECTION INTERVAL Choose as a protection interval the spray interval known from experience to provide scab control. It may be fixed through the season or changeable at various points in the season. The protection interval will be the minimum interval between sprays. In the AU-PECAN project a protection interval of 10-14 days pre pollination and 14 days post pollination was used for Desirable. If a tighter spray interval is used in wet years compared to dry years, use the wet year interval and allow AU-PECAN to detect dry periods where the schedule can be expanded. In orchards requiring more than one day to spray the protection interval begins on the FIRST day of spraying.
  3. SPRAYING BY AU-PECAN Operation of AU-PECAN is based on recorded rain events and the 5-day average forecast of more rain. A rain event is 0.1" of RAIN in a 24-hour period or FOG forming before 8:00 p.m. To spray by AU-PECAN begin recording rain events and checking the rain forecast on the last day of the protection interval. Any rain events during the protection interval prior to the last day are not counted.

When the protection interval since the last fungicide application has passed a spray is advised when:

  1. No rain has occurred but the 5-day average = 50% or greater. OR
  2. One rain event has been recorded and the 5-day average is 40% or greater. OR
  3. Two rain events have been recorded and the 5-day average is 20% or greater. OR
  4. Immediately after three rain events.
  1. TIMING FIRST / LAST SPRAY:
  1. Begin tracking rain events at bud break and spray when model is satisfied if average temperature (avg. of daily min/max) is 57oF or greater. Cold weather is not favorable for scab development and sprays are not advised when temperature is below 57oF. OR (BUT)
  2. 2. Make a protective treatment at parachute stage regardless of weather and begin AU-PECAN protection interval model here. AND
  3. Scab sprays are not advised after shell hardening.
  1. AU-PECAN LIMITATIONS:
  1. AU-PECAN is best suited to operations that can be sprayed in 5-7 days or less.
  2. AU-PECAN is not recommended for operations requiring 7 days to spray over.
  3. Scheduling labor may be a problem in some cases. Once protection interval has passed operations for the day depend on the rain gauge and forecast.
  4. Integrating other pest management needs.
  5. AU-PECAN is not a substitute for management. It is critical to know what is happening in the field so that protection intervals can be adjusted as needed. AU-PECAN, like any fungicide scheduling program, will be most successful when tempered with good judgement.

You will find more information about the AU-PECAN program at http://www.awis.com/

Prepollination

Pecan scab, caused by the fungus Cladosporium caryigenum, is most damaging pecan disease. Scab attacks the foliage, twigs, and developing fruit, causing lesions on leaves as small, charcoal gray to black, concentric circles. Severe infection causes defoliation, fruit abortions, and poorly filled fruit, thus reducing yields. It is active throughout the growing season and, if left unchecked, can cause near total crop losses. Fungal spores, from infected material on the ground, are carried by air currents into the trees. Foliage is susceptible during periods of rapid leaf expansion. Nuts are also susceptible and are poorly filled. Rainfall exacerbates the spread and severity of the disease. The disease continues to be a problem, particularly for the primary commercial pecan tree varieties --Desirable, Schley, and Stuart --grown in the Carolinas, Georgia, Alabama, Florida, Mississippi, Louisiana, and east Texas, where the climate is generally moist. Some resistant varieties are available but, since pecans live a long time, this option is practical only in new plantings. Orchard floor cleanup is useful, by disking for faster decay in soil, but tillage can cause other problems (e.g., root injury and increased loss of soil moisture).

(for more information, see http://www.ars.usda.gov/is/AR/archive/aug98/scab0898.htm)

Downy spot attacks only pecan leaves. Infection reduces photosynthesis and may cause defoliation. Tree vigor and yield are reduced. An effective pre-pollination spray program is critical for control of downy spot.

Dodine, triphenyltin hydroxide, propiconazole, and fenbuconazole are recommended for prepollination applications to control pecan scab and downy spot. [note: triphenyltin hydroxide and propiconazole are often sold and applied in combination. Fenbuconazole and triphenyltin hydroxide are also often applied in combination]

Postpollination

Pecan scab remains a threat throughout the season.

Powdery Mildew causes immature leaves to become distorted. A white layer forms that reduces photosynthesis and/or causes early defoliation. Nuts may also turn color. Problems are typically less severe in older orchards. Additionally, pruning and planting rows with prevailing winds may reduce disease pressure by facilitating improved air circulation. Some pecan varieties also have some degree of resistance to powdery mildew.

Preventative fungicides applied for pecan scab usually keep powdery mildew from being a problem.

Zonate leaf spot, causes severe defoliation of pecan trees during July and August of rainy summers. Leaf spots on the upper surface of pecan leaves are grayish brown, with concentric ring formations that are more distinct on the lower side of the leaf. Leaf spots on the lower surface are light brown in the center, becoming darker brown toward the edge. The fungus requires moisture to develop, growing most rapidly when the leaves are wet. No resistant pecan varieties have been identified.

To control scab and powdery mildew, fungicides applications are recommended at 14-21 day intervals from pollination until shell hardening. In orchards with any scab on nuts by mid-June or where more than 10% of nuts have scab by early July, the spray interval should be no more than 14 days until shell hardening.

On pecan varieties with a summer growth flush, a fungicide application should be made within 10 days of the growth flush.

If the five-day weather forecast shows a high probability of a system that will produce several days or rain, the fungicide should be applied to as much acreage as possible before the rain begins.

Dodine, triphenyltin hydroxide, propiconazole, fenbuconazole, and azoxystrobin are recommended for prepollination applications to control pecan scab and powdery mildew after pollination. [note: triphenyltin hydroxide and propiconazole are often sold and applied in combination. Fenbuconazole and triphenyltin hydroxide are also often applied in combination] Sulfur may also be used in combination with fungicides (sulfur cannot be used with dodine) to control powdery mildew.

Triphenyltin hydroxide combined with benomyl or thiophanate methyl is recommended to control zonate leafspot. Benomyl and thiophanate methyl should not be used alone. A one-half rate of triphenyltin hydroxide may be used in orchards where scab resistance to benomyl or thiophanate methyl has not occurred.

After shell hardening

Pecan scab continues to be a threat.

Zonate leaf spot and other leaf diseases may also be a problem.

Pesticide applications may be recommended based on scouting reports. Recommended pesticides are the same as earlier season applications.

Fungicides used on Georgia pecans (USDA Agricultural Chemical Usage, Fruit & Nut Summary, 1999)

Fungicide

Percent crop treated

# applications

Rate/application lbs/acre

Rate/crop year lbs/acre

fenbuconazole

23

4.0

0.07

0.28

propiconazole

69

5.2

0.11

0.6

sulfur

20

1.4

2.87

4.04

triphenyltin hydroxide

83

5.8

0.25

1.48

 

 

Weeds

Uncontrolled weeds interfere with tree growth and may interfere with irrigation and harvesting. A clean orchard floor is imperative for efficient harvest of nuts. Most operations use a tractor-mounted hydraulic tree shaker to dislodge nuts from the trees. Then nuts are swept into rows on the ground for mechanical pickup. Bare soil or closely mowed grass makes this system possible.

Herbicides are primarily used control weeds under the trees. The shade produced by the tree canopy also inhibits weed growth. Mowing and tillage are often used to control weeds between the tree rows. Tillage near the trees is likely to cause root injury to the trees.

Herbicides used on Georgia pecans (USDA Agricultural Chemical Usage, Fruit & Nut Summary, 1999)

Herbicide

Percent crop treated

# applications

Rate/application lbs/acre

Rate/crop year lbs/acre

diuron

21

1.2

1.12

1.42

glyphosate

73

2.5

0.6

1.52

paraquat

32

1.4

0.32

0.46

 

 

References

  1. Based on information developed by HC Ellis (UGA Extension Entomologist) Paul Bertrand (UGA Extension Plant Pathologist), Thomas F. Crocker (UGA Extension Horticulturist), and Stanley Culpepper (UGA Extension Weed Scientist)

  2. 2001 Georgia Pecan Pest Management Guide by HC Ellis, Paul Bertrand, Stanley Culpepper, and T.F. Crocker.

  3. Georgia Pest Control Handbook. Available on the web at http://entomology.ent.uga.edu/Publications/publications.html

  4. Georgia Agricultural Facts. http://www.nass.usda.gov/ga/pubpages/agfacts.htm

  5. USDA Agricultural Chemical Usage, Fruit & Nut Summary. http://usda.mannlib.cornell.edu/reports/nassr/other/pcu-bb/

  6. Prepared by Paul Guillebeau, IPM/Pesticide Coordinator, Department of Entomology, University of Georgia, Athens GA 30602 pguillebeau@bugs.ent.uga.edu