Pecan Basics

• Pecan Tree
• Production History
• Insect Pests of Pecan
  • Insect Pests of Nuts
  • Insect Pests of Foliage
  • Insect Pests of Trunk and Branches
• Beneficial Insects
• Diseases of Pecan
• Cover Crops

Pecan Tree

The pecan, Carya illinoinensis, is a member of the plant family Juglandaceae. This family includes the walnuts and the hickories. Brison, in his book "Pecan Culture," writes that the pecan is the most important horticultural crop native to the United States. The pecan is a large tree, often growing to 100 feet high or more and has a stately appearance. It has been proclaimed the state tree of Texas.

The pecan is indigenous to a large area extending from the Mississippi River Valley on the east to the western branches of the Llano and San Saba rivers of Texas on the west, and from southern Illinois in the north to northern Mexico in the south. Isolated populations also occur in Alabama, far west Texas, and Mexico. These may be important sources of diversity that can be used in pecan breeding. Unlike other horticultural crops, the native pecan is very important commercially.

Pecan Production History
Pecans are produced on about a million acres worldwide.  Annual production usually averages between 200 and 300 million pounds. However, unlike most cultivated crops, the domestication of the pecan only began late in the last century and much genetic potential remains to be capitalized upon. Furthermore, wild pecans in Texas, Oklahoma, Arkansas, Louisiana, and Mexico are perfectly acceptable in the marketplace -- so much so that Texas production consists of about 55% wild and 45% improved in an average year as of 2005.

Worldwide pecan (nut) production generally exceeds 250 million pounds per year. The pecan has been introduced to foreign countries such as Israel, South Africa, Brazil, and Australia, as well as states on the Eastern Seaboard. Georgia, which had no pecans a few hundred years ago, has within the last 75 years become the leading pecan producer in the U.S. Texas production averages about 35 million pounds per year.

History of pecan and factors affecting arthropod management:

Prior to 1800
Native Americans gathered and subsisted on pecans; early explorers and settlers readily adopted them to their diets.

1800 to 1900
Settlers thinned tree stands in native range leaving pecans and grass for grazing. Seedling orchards established in southeastern U.S. Grafting technology for pecan developed but not heavily implemented until end of century. Rail transportation results in shipment of nuts to urban markets.

1900 to 1930
Vegetative reproduction inundates southeastern U.S. with many selected varieties.
Bordeaux spray 3-10 times recommended for nursery trees to prevent scab but large orchard trees considered unreachable. Plant resistant trees like Stuart, Schley and Frotscher. Early harvest, sanitation, burning and Persian insect powder used for insect control.

1930 to 1940
Shelling machinery, transportation and consolidations of orchards into economic units increase marketability of pecans.

Expanded production of most popular varieties like Stuart met with increasing levels of pecan scab on previously resistant varieties. Rosette linked to foliar zinc deficiency; lead arsenate and nicotine sulfate recommended for insect control. Spray machinery expensive, labor intensive and rarely employed.

1940 to 1950
Tank mixing of nicotine sulfate with needed fungicides recommended as "cheap insurance." Contract spray services expand with truck-mounted hydraulic sprayers. DDT used for pecan nut casebearer but aphids and mites appeared in epidemic numbers; toxaphene alone or mixed with nicotine sulfate controlled pecan nut casebearer without resurgence of aphids and mites.

1950 to 1960
Airblast speed sprayers become available; compared to hydraulic sprayers, cheaper speed sprayers allow single operator to spray same number of trees with one-fourth the water and still obtain better coverage. Effective and economical rosette, arthropod and pathogen control with conventional and newer chemicals resulted. Malathion adopted for pecan nut casebearer control. Chemical management of pecans became widespread.

1960 to 1970
Cyprex and then Du-Ter replaced Bordeaux for pecan scab control and new carbamates, organophosphates and systemics became available for arthropod control. Mechanization for pesticide application, pecan maintenance, harvesting and processing burgeoned along with explosion of chemicals and solutions appeared faster than problems. Chemical schedules became routine and screening for efficacy dominated research efforts.

1970 to 1980
Chemicals and Resistance
Carbaryl became chemical standard for pecan weevil management, phosalone for other arthropods, Benlate and Du-Ter for pathogens, and NZN or zinc sulphate + uran for rosette. First case of pesticide resistance in pecan was a pathogen (causal agent for pecan scab) to Benlate in 1975, followed by hickory scorch mite resistance to carbamates and organophosphates in 1979.

Synthetic pyrethroids introduced late in decade. Integrated Pest Management (IPM) philosophy develops and spreads across agriculture due to widespread pesticide resistance by arthropods, secondary pest outbreaks like aphids, mites and leafminers due to broad spectrum pesticides killing natural enemies and societal concerns about environmental pollution.

Pecan industry buffered from many of these problems because of the surfeit of chemicals for all pests and lagging problems of resistance due to remaining management diversity. Aphids were viewed as a major problem in El Paso Valley of Texas and increased reliance on natural control by predators and parasites resolved their problem.

Pest Management
Increased attention paid to developing economic thresholds of important pests, refining understandings of basic biologies to predict and manage pests, to identify and rely on natural enemies of pests and other IPM strategies. Pecan IPM programs initiated in Alabama, Georgia, Texas and elsewhere late in decade. Widespread expansion of new pecan plantings of a few varieties occurred in Southwest and Mexico inside and outside the native range epitomizing the drastic narrowing of genetic diversity in the natural pecan population compared to cultivated varieties.

1980 to 1990
Arthropod resistance to pesticides becomes widespread and Federated Pecan Growers declare aphids the most destructive pest in 1985, refuting the contention that the pecan industry had adopted IPM without the normal cycle of subsistence, exploitation, crisis, disaster and finally integrated control.

Modeling efforts and basic biological studies on pecan nut casebearer, pecan weevil, hickory shuckworm, pecan aphids, pecan scab and other pests began to be implemented into management programs.

Phosalone withdrawn from market in 1989.

Implications of continued transition from diverse native and seedling trees to increased genetic uniformity of vegetatively propagated varieties on ability to manage diseases and arthropods became ever more apparent, continuing a trend observed at least half a century earlier.

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Beneficial Insects

Wheel Bug
Nymphs or the immature stages of the wheel bug, Arilus cristatus can be found on pecan trees at this time. The immatures have red abdomens, and black heads, legs and thorax. The early immature stages can be found clustered together near the egg cases. As these immatures develop they will disperse through the tree. These insects feed on a wide range of soft bodied insects and are considered beneficial.

Wheel bug,
Arilus cristatus,
adult on leaf.
Photo by Bill Ree.

Wheel bug,
Arilus cristatus,
nymphs on tree.
Photo by Bill Ree

Wheel bug,
Arilus cristatus,
nymph on leaf.
Photo by Bill Ree.

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Cover Crops

The establishment of a cover crop between rows of trees combined with an herbicide treatment to remove vegetation leaving a bare circle beneath each tree is practiced by many producers.

A variety of clover is the typical choice of cover crops. Many varieties are available and the best one (or mixtures) for your area depends on soil type and climate. Tibbee Crimson, Bigbee Berseem, and Hairy Vetch have been used effectively in some areas but there are dozens of others to consider as well.

The county agent in your area will be the best first contact to determine which cover crop will best suit your needs.

Advantages and Disadvantages

Vetch

Advantages of a legume cover crop are:
1. Providing vegetative cover to reduce erosion especially through the spring
2. Providing habitat for natural enemies during the spring
3. Returning nitrogen to the soil where legumes are used
4. Reducing competition for nutrients and water during summer months when the legume cover crop goes dormant

Disadvantages of a legume cover crop are:
1. Investment to identify the best cover crop
2. Establish and maintain the orchard floor
3. Grazing is still possible but precautions must be taken to prevent bloating
4. Cycling of cattle on and off the orchard varies compared to grass cover