Crop Profile for Pecans in Texas

Revised: June, 2002

General Production Information

Texas is the second largest producer of pecans in the U.S, producing 30-90 million pounds. Pecan is the most economically important member of Carya, which includes hickories and walnuts.
Pecans provide $62 million for growers and generate over $200 million in the Texas economy. Improved varieties and native are grown on more than 170,000 acres and are grown in 50 counties in Texas.
Since Texas was the geographic origin of the pecan species (Carya spp.), most of its pests co-evolved in the same region with the present-day crop. Cross pollination traits are considered in planting orchards since male and female flowers mature at different times in the same tree.
Since the 1980s, growers have reduced insecticide use by 35%, fungicide use by 30%, and total applications by 9% due to wide scale implementation of IPM practices.
Stands of improved varieties ("orchards") are planted to 35 trees per acre and then progressively thinned over 40 - 80 years to 4 to 8 trees per acre.
Improved pecans make up 40% of the acreage but provide 60% of the total nut production. Yields are higher, the grafted lines produce a more desirable nut, and returns to production inputs (including pest control) are greater. Native pecans commonly grow on alluvial soils near rivers and creeks.
Nuts that are examined are "flagged" so scouts can re-examine same site for additional eggs laying, to monitor developmental progress. Scouts return to flagged sites to examine eggs and look for new development. Traps are placed in early April. Workers examine nut clusters, traps, and foliage for emergence; egg laying follows in 7 days, then spraying starts. Check again in 3-4 days.
Most insecticides do not have clearance for grazing livestock, except malathion, Bt, & carbayl. Mechanized harvesting is practiced on 75% of the crop. Native pecans are not irrigated. Drip irrigation is practiced in some planted groves.

Insects

Most common pests:

Nut damaging- pecan nut case bearer, & pecan weevil
Foliar pests- pecan aphid, caterpillar, webworm

Common insecticides: chlorpyrifos/ Lorsban , carbaryl, and tebufenozide/Confirm.
35% less insecticide is now applied as a result of IPM programs.
See Table 1 for details.

Diseases

Most common: pecan scab, powdery mildew, stem-end blight.
Most common fungicides: propiconazole (Tilt) and triphenylin hydroxide.
90% of Texas' 170,000 acres is sprayed with one or more fungicides.
See Table 2 for details.

Weeds

Most common weeds: Perennial weeds, bermudagrass.
Herbicides: used sparingly, mostly glyphosate to control weeds under trees.
See Table 3 for details.

Worker/Exposure Issues

Exposure to pesticides is minimal since most tasks are mechanized or done in when pesticides are not applied.

Table 1. Summary of Pesticide Use in Texas

Pesticide	Total lbs ai/yr	% of total
Insecticides (chlopyrifos, carbaryl)	493,300	66
Fungicides (propiconazole, organotin)	227,900	31
Herbicides (glyphosate)	21,800	3
TOTAL	743,000	100

Field Tasks	Worker exposure
January - February Complete nut harvest. Thin or remove crowded trees.	No pesticide use. Workers on site
March - April Spray herbicide between trees. Apply fertilizer and zinc to mature trees. Begin grafting new trees. Spray Pecan phylloxera at bud break (April) Spray fungicide for scab.	Ground sprayers Tractor equipment Hand work Minor problem Variable with location
May - June Monitor casebearer pheromone traps daily. Apply nitrogen and zinc. Irrigate according to water needs. Spray herbicide down tree row; shred middles. Spray casebearer. Spray fungicide if needed.	Scout traps. Ground sprayers. Some irrigation conducted Tractor work Variable with location Variable with location.
July - August Collect leaf tissue samples. Continue irrigation for kernel filling. Fertilize if needed. Shake trees to thin nuts. Apply a fungicide if needed after rains. Place weevil traps, monitor, and spray if needed. Spray pecan weevil, shuckworm, stink bug & black aphid.	Scouting Some irrigation conducted Variable with location Tractor work Variable with location Scouting in orchards. Variable with location
September - October Continue irrigation. 2^nd pecan weevil application, 10 days after 1^st if needed. Monitor weevil emergence, spray if needed. Prepare soil and remove fallen limbs for harvest. Harvest nuts when shucks open.	Some irrigation conducted Variable with location Variable with location Hand work Scouting
November - December Continue nut harvest	No applications.

Summary:
"Scouting" is the most significant re-entry activity after insecticide application. Insecticide and fungicide treatments are usually completed 7 days or more before harvest.

Insect Pests

Background

Several nut-damaging and foliar-feeding insects attack pecans. Damaged nuts reduce yields or contain insect parts or frass which are unacceptable to consumers. Foliar insects feed on photosynthetic tissue at critical times and reduce yields or nut quality.
Probably no other crop has the demonstrated success of pecans in the practical use of IPM tactics to reduce pesticide use. .
Insecticides are frequently applied in combination with fungicides. Improved pecans are usually sprayed twice for nut damaging insects and once for foliar pests.
Diflubenzuron (Dimilin), an IGR that disrupts insect development, offers new soft chemistry for non-target insects & protects beneficial insects. The pending registration will offer the pecan industry alternatives to present chemistry.

Nut-damaging insects

Pecan nut casebearer

The most damaging insect in pecans, caused by larva feeding inside the nuts.
Emergence from overwintering is monitored by pheromone traps are placed 3 to 5 per 50 acres. Spraying initiated at one or more eggs per 100 flower clusters. Infested clusters then are flagged to monitored for egg hatch. Insecticides usually are applied with ground sprayers in 100 gallons per acre for effective coverage.

Pecan Weevil

Most damaging late in the season. Adults, feeding emerge in early August and begin on nuts. Weevil emergence and populations are monitored with one of several different types of traps.
Damage occurs for females laying eggs in the nut (at dough formation stage).

Hickory Shuckworm

Mid- to late-season pest, tunnels into shucks, disrupts nutrient flow, and nuts stick to shucks, fail to fill, and reduce yields. 50% or more of the acreage is sprayed twice with Chlorpyrifos/Lorsban.

Stink Bugs

Stink bug and leaf-footed bug build up on other crops or weeds and then migrate to pecans to suck sap from developing nuts. An insecticide treatment of small plantings of a trap crop, such as blackeyed peas, kill the critters before they cause damage in pecans. Sprays for other pests also suppress stink bugs.

Foliar Insect Pests

Aphids

The black pecan aphid is more destructive yellow aphid. Aphids suck water and plant nutrients from foliage. Outbreaks can cause defoliation. The black aphid injects a toxin that discolorates leaves.
Important insecticides for black or yellow aphids include dimentholate, chlorpyrifos/Lorsban, esfenvalerate/Asana, and imidaclopid/Provado.

Walnut caterpillar and Fall Webworm

Feed on pecan foliar and sometimes require chemical treatment when natural controls are not adequate. Fall webworms form silken webs. Spot treatments are sometimes effective.
Insecticidal control involves scouting for timing and infestation levels for the use of Bt, carbaryl, chlorpyrifos, malathion, confirm, spinor, and tebufenozide.

Other Insect Pests

Red Imported Fire Ants

Fire ants attack orchard workers when grafting buds, mowing weeds, harvesting, and other operations. Ants come to drip irrigation lines for moisture and cause damage to equipment and emitters. Fire ant control includes juvenile hormones (JH), insect growth regulators (IGR), and other control agents- which are beyond the scope of this profile (see Texas Ag Extension Service Bulletin 1536 on Fire Ants and Their Management).

Table 1. Summary of insecticide use in pecans¹

Insecticide	Application (lb ai/ acre)	Applications per year	% of treated acres²	Total lb ai applied/year	Comments
Nut pests:
carbaryl	3.0	2	30	306,000	Some rotation with cypermethrin for weevils.
Sevin:
chlorpyrifos	1.0	2	10	136,000	Used in rotation with tebufenozide or phosmet.
Lorsban:
cypermethrin (Fury)	0.05	2	10	1700	May cause aphid outbreak.
phosmet	1.5	1	5	6,200	Used in rotation with carbaryl.
Imidan:
tebufenozide (Confirm)	0.25	2	30	24,000	Used in rotation. May add carbaryl if weevils present.
Foliar Pests:
esfenvalerate (Asana)	0.04	1	10	700	Pyrethrins are excellent for aphids. Low costs, low rates.
B.t.	N/A	1	1	N/A
imidacloprid (Provado)	1.0	1	1	1700
malathion (several)	1.0	1	10	17,000	Used where livestock may graze.
TOTAL				493,300

¹Insecticide application may be included with zinc and fungicide sprays based on insect scouting and trapping.
²Based on chemical use in the 170,000 acres of commercial pecans planted in orchards.

Diseases

Background

Control of most pathogens requires a combination of cultural practices and judicious use of fungicides. The most damaging disease is pecan scab. Other diseases are usually controlled when pecan scab treatments are applied or are not economically important.

Pecan scab

Foliage is susceptible during periods of rapid leaf expansion. Nuts are also susceptible and are poorly filled. Good drying and air flow are important.
A litter free orchard floor is useful but tillage damages roots and increases irrigation needs

Powdery Mildew

Immature leaves become distorted and a white layer forms and reduces photosynthesis or causes early defoliation. Fungicides applied for pecan scab keep powdery mildew from being a problem.

Stem-end Blight

Several fungicides are effective one application is adequate most seasons. Scab treatments usually keep stem-end blight from being a problem.

Other Diseases and nematodes

These include shuck dieback, downy spot, fungal leaf scorch, several leaf spots, leaf blotch, galls and cankers, and kernel decay (McEachern and Stein, 1997) are other pathogens that cause disease and economic losses in pecans.

Several nematodes feast on pecan roots. Infected trees may produce foliage that appears as being zinc deficient. Planting stock is carefully selected to avoid planting infested material. Soil treatments after planting not used.

Fungicides and their use

Fungicides are best used as preventative treatments to protect plant foliage and are applied before the on-set of periods of leaf wetness. Eradicant or corrective treatments are seldom successful. Treatments are usually 'rain fast' after 4 hours.
Over 70% of the fungicides are applied with ground equipment. Sprayers must penetrate the canopy to assure good coverage. Aerial application is practiced on 30% or less of the crop and is used when soil is wet. Aerial application is less effective in penetrating the canopy but is essential in wet weather.
Fungicide use in improved pecan orchards is summarized in Table 2. Use of all fungicides total.
Stragego fungicde, was registered in 2002 and combines the complementary chemistry of propaconazole and trifloxystrobin, to control pecan scab and anthracnose. Longer lasting disease control is expected on foliage and nut shucks. An extended 14 to 21 day spray interval may now by possible.

Table 2. Fungicide use improved pecans in Texas, primarily as preventative for pecan scab

Fungicide	Application (lb ai/ acre)	Applications per year	% of acres treated¹	Total lb ai applied /yr	Comments
propiconazole (Tilt)	0.1	3	80	40,800	Used less in west
triphenylin hydroxide (Super Tin)	0.37	3	50	94,350	Applied as Orbit.
azoxystrobin (Abound)	0.17	3	10	8,670
fenbuconazole (Enable)	0.11	3	20	11,220
thiophosphate methyl (Topsin)	0.7	3	5	17,900	Usually rotated in resistence mgt.
TOTAL				172,940

¹ This date covers the 170,000 acres of improved pecans in managed orchards. The 600,000 acres of native pecans receive little or no fungicide treatment.

Weeds

General:

Vegetation is generally managed so that weedy plants do not affect tree growth, adversely impact irrigation systems, or interfere with mechanical harvest.
Tillage is practiced between tree rows to control weeds. However, crop roots are pruned if the tillage is close to trees. Plastic mulches are seldom used, due to intense sunlight in new plantings. Once a shade canopy is established, the reduced light does not favor weed growth.
In the western areas, where trees are drip irrigated, the areas between the tree rows are tilled to control weeds. In eastern areas, where rainfall is higher, tillage and herbicides are used in combination.
While eight or more herbicides are labeled for use in pecans, less than 22,000 pounds ai are applied per year. Glyphosate makes up nearly 70% of the total and six soil-applied herbicides make up 25% (see Table 4).
Vegetation management is particularly important for mechanical harvesting. 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.

Herbicide Use:

Several herbicides are labeled for use in non-bearing and/or bearing pecans. However, the primary use is for postemergence control of weeds under the shade canopy.
Little or no herbicide is used in the 600,000 acres of native pecans found along stream beds since the tree canopy shades out most weeds and there is little advantage to treat these areas, which are usually grazed by livestock or prone to flooding
Soil-applied herbicides are used on less than 4% of the total 170,000 acres of pecans. Trifluralin and pendimethalin are used more frequently than others but no single herbicide predominates the market. Use rates range from 0.5 to 1.0 lb ai/A.
In the postemergence market, glyphosate is used in 45% of orchards, in a 20% band (actual width depends on row spacing), and in the tree row at 0.5 to 1.0 pound ai per acre, for a total of 7500 to 15,000 total pounds in the Texas pecan industry. Clethodim is used at 1 lb ai/A in a 20% band on less than 3% of the acreage.

Table 3. Herbicide use in pecans in Texas

Common name	Trade name	Application (lb ai/ acre)	% of acres treated	Application (lb ai/ year)
Soil Applied		0.5 to 1.0	5 to 10	5,100
trifluralin	Treflan
pendimethalin	Prowl
simazine	Princep
diuron	Karmex
oxyflurofen	Goal
halosulfuron	Sempre
Postemergence
glyphosate	Roundup & others	1.0	45	15,000
clethodim	Select	1.0	3	1,700
Total - 8 herbicides				21,800

Contacts

Dudley Smith
Department of Soil and Crop Sciences
Texas A&M University, College Station, Texas, 77843-2474
dt-smith@tamu.edu

Marvin Harris
College Station
IPM practices in pecans
m-harris@tamu.edu

Thomas "Chip" Lee
Stephenville
Extension Plant Pathologist
t-lee@tamu.edu

George McEachern
College Station
Extension Pecan Specialist
g-mceachern@tamu.edu

Bill Ree
College Station
Extension Entomologist
w-ree@tamu.edu

References

Harris, M.., B. Ree, J. Cooper, J. Jackman, J. Young, R. Lacewll, and A. Knutson. 1998. Economic impact of pecan pest management implementation in Texas. J. of Econ. Ent. 91: 1011- 1020. [25-year summary of IPM programs and impact in pesticide use.]
Harris, M. 1985. Understanding pecan IPM. Pecan South. 6p. [Overview of pecan pests and resistance management in pecans.]
Knutson, A., and B. Ree. 1998. Controlling the pecan nut casebearer. Texas Agri. Ext. Serv. Leaflet 5134. 5 p.
Knutson, A., and B. Ree. 1998. Managing insect and mite pests of commercial pecans in Texas. Texas Agri. Ext. Serv. Bulletin 1238. 14p. [A practical summary of insect pest management.]
Lee, T. A. 2000. Home page, displaying photographs of pecan diseases and control measures.
http://stephenville.tamu.edu/~CLee/pecandis.htm. [Excellent display of diseases.]
McEachern, R., and L. A. Stein. 1997. Texas pecan handbook. Texas Agri. Ext. Serv. Handbook 105. [Several chapters on pests, monitoring and non-chemical practices, and pesticide use.]
Philley, G.L. 1998. Fruit and nut disease control products for use in Texas. Texas Plant Disease Handbook. b. 1104. [Overview of disease control measures.]
Ree, B., A. Knutson, and M. Harris. Controlling the Pecan Weevil. Texas Agri. Ext. Serv. Leaflet 5362.