How Can I Manage Pecan Pests?
During the fall we get many questions about problems with pecans. Pecans are subject to attack by more than 20 insects and mites. However, in North Carolina, only 4 insects are important. These are the pecan weevil, twig girdler, stinkbug, and aphids. Scab is the only disease of major importance.
The pecan weevil is the most serious pest because it attacks the nut. Pecan weevils first puncture the nuts. After being punctured, the nuts may fall within 2 to 3 days. The second damage is from larval feeding in the nut. At larval maturity, larvae chew a circular hole through the shell. When the nuts fall to the ground, the larvae exit the nut and burrow into the soil. Most of the questions are about what causes these holes.
Adult weevils have long slender snouts and thin legs. Weevils are reddish brown to gray and about 1/2 inch long. The snout is longer than the body on females and shorter on males. Larvae are white, legless grubs with red-brown heads. I have seen some pecans with up to five of these grubs per nut. The second stage of development is the pupal stage. Pupae develop underground below the trees they damage. Adults emerge from the soil from August through September. Often they emerge following a rainfall of 1 inch or more. Adults mainly crawl or fly into the trees, mate, and live for many days. Females chew holes into nuts where they lay eggs. At maturity the larvae exit the nut and burrow into the soil where they remain for one to two years.
Monitoring for weevils is done in late summer by wrapping burlap around pecan trees 3 to 4 feet above the soil and tying it at the bottom. The remaining burlap is overlapped and then tied at the top, causing the weevils to walk over each flap and allowing time for grower observation. In commercial situations, sprayable formulations of insecticides are sprayed up in trees with large air blast sprayers to control pecan weevils. However, at home this is not feasible. To limit the numbers of weevils, treat the lawn area under the trees with Sevin Lawn Insect Granules (most home garden liquid formulations are not labeled for home gardeners to spray trees) following a heavy rainfall in August. This product does have to be watered in after application. A second application 10 to 14 days later will improve control. Follow label directions for treatment of lawns for beetles or grubs.
Southern green stinkbugs attack the nuts. It is a large green shield shaped bug. If they feed before shell hardening, the nuts fall early. If they feed after shell hardening, black spots develop on the kernel that are bitter. Stinkbugs over-winter in debris in the orchard, so keep the area mowed and clean of debris.
The pecan twig girdler is a large beetle with long antennae. Females lay clear eggs in slits in twigs they girdle half way through. These branches fall to the ground when the force of the wind breaks the remainder of the twig in September or October. Larvae feed in the twig and then enter the soil. Picking up these girdled twigs as soon as they fall is the best way to reduce the population next year.
Yellow and black aphids feed on pecan leaves. Aphids have soft bodies, delicate wings, and a pair of tubes projecting from the abdomen. As they feed they deposit honeydew, which a sooty mold fungus grows on and turns the upper leaf surface black. Damaged leaves have speckled areas that turn brown. Heavily infested trees exhibit early leaf fall. Young aphids are wingless and appear in large numbers. Both aphid types over-winter in bark cracks. It is difficult for a homeowner to spray a large pecan for aphids. Don’t park your automobile under pecan trees to avoid the black spots created when sooty mold grows on the honeydew dropped by aphids.
Pecan scab is the major disease concern in pecans. It is a fungus that attacks the leaves and the shuck. The disease affects young leaves and causes small circular spots that enlarge causing the leaf to be deformed. Lesions on nut shucks appear as small sunken black spots and in severe cases may turn the entire shuck black and . Some shucks will fall prematurely and later infections may cause the shucks not to release properly. Pecan scab is managed by selecting resistant varieties in the home orchard. Pecans with high scab resistance include: Sumner, Elliot, and Gloria Grande. Moderately resistant varieties are Cape Fear, Stuart, Chickasaw, and Kiowa.
If you have questions about your home garden, lawn, landscape or trees call the Extension Master Gardener Volunteers at 902-1705 or email questions to firstname.lastname@example.org. They will be at the Pitt County Farmers Market today from 7:30 to 11:30 am as well. You can find more gardening information at http://pitt.ces.ncsu.edu.