Fruit-Insect Pest Management

Insect Note #P-2 (Revised)

Prepared by:
K. A. Sorensen, Extension Entomologist

Dated 1/94
Placed on the Web 4/95 by the Department of Entomology, NCSU
Revised: 2/17/05

Pecan Insects and Their Management

Pecans in North Carolina are subject to attack by over 20 insects and mites. However, only four insects, the pecan weevil, twig girdler, stink bug and aphids are of economic importance in most years. It is critical that commercial growers and homeowners be able to recognize damage by these insects, understand their life history, employ insect monitoring tactics and subscribe to Integrated Pest Management strategies.

Insect/Damage Recognition and Life History

The pecan weevil is the most serious late-season pest, as it attacks the nut. Its hosts include pecan and hickory. Adult pecan weevils are beetles with long slender snouts and thin legs. They are reddish-brown to gray and between 0.3 to 0.5 inch long. The snout is longer than the body on the females and slightly shorter on the males. Eggs are white and are laid inside the developing pecan nuts. Larvae are creamy white, legless grubs with reddish brown heads. They have four stages and when full grown are 0.35 inch long. Pupae develop underground and are seldom seen.

Pecan weevils cause two types of damage. When they emerge from the soil in August, they puncture nuts. This feeding causes nuts to fall in 2 or 3 days. The second type of damage is larval feeding within the nut. At maturity, the larva chews a circular hole through the shell and exits.

The life cycle of the pecan weevil consists of 4 stages and can span 3 years. Adult weevils emerge from the soil from August through September. Often a rain of 1 inch will trigger emergence. Adults crawl or fly, mate and live for many days. Females drill holes into nuts and lay eggs. Larvae pass through 4 stages feeding inside the nut. Nuts drop to the ground and larvae exit. They burrow into the soil where they remain for 1 or 2 years. They pupate and change into adults about 3 weeks later and remain in the soil until next August.

Both southern green stink bugs and leaf-footed bugs attack pecan nuts. They puncture nuts before shell hardening and after shell hardening. If feeding is early the nuts drop.

If the feeding is late then black spots or pits develop in the kernel. This damage is referred to as kernel spot or bitter pit.

The southern green stink bug is large, green, shield-shaped and about 0.5 inch long. Adults have wings and nymphs are wingless. The leaf-footed bug has a narrow body and long leaf shaped hind legs.

Both species overwinter as adults in debris. They emerge in the spring and lay eggs in grasses or soybeans. They move to pecans only as adults. There are four or five generations a year. Nymphs develop on grasses and vegetable crops.

The pecan twig girdler is a large beetle with long antennae that girdles twigs and small branches in September. Females lay clear glassy eggs in slits in the girdled branch. These branches fall to the ground when the wind blows. Larvae feed in the branch and exit to pupate in the soil. There is only one generation a year.

Two species of aphids attack pecans. Yellow and black aphids feed on leaves. Honeydew is deposited on the foliage and black sooty mold fungi develops. Damaged leaves may appear speckled or have patches that often turn brown and then die.

Adult aphids are either yellow or black and have soft bodies with delicate wings and a pair of tubes projecting from their abdomen. Adults have wings and immatures are wingless and usually appear in colonies.

Both species overwinter as eggs deposited in bark crevices. Nymphs are active in the spring. There may be 10 or more generations a year. Damaged leaves may appear speckled or have yellow patches that often turn brown and then die. Such feeding can cause leaves to drop prematurely.

Insect Monitoring

Monitoring in a systematic way allows one to know what pest and beneficial insect population levels exist in an orchard as well as where and when. Two monitoring techniques used in pecans are field surveys and insect trapping. In sampling for foliar insects one randomly selects 5 compound leaves and 5 nut clusters from five trees in a 10 acre block. Samples can be taken weekly and look for any and all problems as you walk the orchard. Record observations and refer to these regularly to determine relative comparisons and trends. It helps to mark your trees with a number so you can have a reference point.

Insect traps are used to catch pests and monitor their relative development and trigger additional sampling. Traps can also be used to time sprays. A black-light insect trap can be used for moths, beetles and stinkbugs. They should be suspended on a pulley and operated some 20 feet in the tree canopy. Pheromone traps containing a sex attractant are also available for many insects. They are species specific. There are 2 ways to monitor for pecan weevils using traps. First is by placing cone cage traps under tree drip line and recording the number of adult weevils collected. A second way is to use trunk band traps. Burlap bags can be wrapped around tree trunks of several trees in an orchard. Daily collections and destruction of male and female weevils indicate when to spray as well as provide some physical control.

Another method of monitoring pests in general is to place a sheet of plastic or cloth on the ground under trees. Trees can then be sprayed with Pyrethrin, Sevin or Asana application. One can then return and record the insect found on the sheet. One could also jar the tree and look for insects. In the case of twig girdlers, fallen twigs can be examined for the smooth cut surface done by adult beetles.

Some other insects of concern include: casebearers, leafminers, mites, fall webworms, spittlebugs, hickory shuckworm and phylloxeras. For further help in insect recognition control contact your local county Cooperative Extension Office.

Some pecan insect management strategies and tactics follow:

Establish a new planting away from wooded areas to discourage insects, squirrels, birds etc.
Do not grow soybeans, vegetables and related crops or weeds nearby, as these plants encourage stinkbugs.
Avoid growing early maturing varieties in low wet areas.
Till the soil or mow the orchard early in the summer to destroy weed hosts.
Provide good horticultural care using soil and foliar samples for fertility indexes and provide adequate moisture during the growing season.
Top work old trees or thin trees to lower fruiting wood and permit spray coverage.
Monitor for aphids and their natural enemies and be prepared to use an aphicide should aphid populations build.
Gather and destroy fallen twigs during September to reduce twig girdler populations.
Frequently gather, remove and destroy weevil-infested nuts as they fall.
Keep areas around the orchard free of debris which harbor overwintering insects.
Follow all recommended practices for successful pecan production and marketing.
Ground sprays of Sevin and/or foliar sprays of Sevin during August are recommended for pecan weevil. Weevil emergence and traps will identify critical periods for well-timed sprays.

For more information, please refer to Fruit Insect Note #P-1, "Insects and Related Pests of Pecan"; Extension Leaflet AG-81, Growing Pecans in North Carolina, and the North Carolina Agricultural Chemicals Manual. Your county Cooperative Extension Office can be of further help.

Figures not included due to poor quality of reproduction.

The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsements by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. All pesticide recommendations provided in this publication apply to pest control in North Carolina. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain information about product usage in your locale and examine a current product label before applying any chemical. The information presented on pest biology is based on conditions in North Carolina and may not be applicable to your locale. For further information, we recommend that you contact the Cooperative Extension Service office in your county.