The pecan, Carya illinoinensis, is a species of hickory tree that is native to the southern United States. The nut is a southern favorite when made into pecan pie. The tree suffers from a number of insect pests, most of which can be countered with pesticides or traps using pheromones as bait.
The Pecan Weevil, Curculio caryae, is a light brown or grayish beetle about ½ inch long and with a long beak. Weevil larvae and adults spend the winter 4 to 12 inches deep in the soil. They emerge during the spring to feed on the pecans before the nut shells harden. Weevils make pin-sized holes as they penetrate the nut, causing it to bleed. Weevil larvae destroy the interior of nuts by feeding on the kernels for several weeks. In late summer, the grubs make round holes in the shell and emerge. The adults drop to the ground in December to repeat the cycle. Horticulturalists at Texas A & M University recommend treatment with insecticides containing carbaryl and zeta-cypermethrin applied according to the manufacturer’s label.
Pecan Nut Casebearer
The Pecan Nut Casebearer, Acrobasis nuxvorella Neunzig, feeds on pecans from Florida to New Mexico. Overwintering Casebearer larvae emerge as moths in May and June. The female lays white eggs on the calyx of the nuts after they are pollinated. White to yellow larvae, about ½ inch long, bore into the base of developing nuts, leaving silk and black excrement where they entered. They feed inside the nut for a month to five weeks, then emerge nine to 14 days later. A bait that mimics the pheromone sex attractant emitted by female moths is used to lure males to a sticky trap. Wasps such as the Basus acrobasidis and other insects may also be used as biological controls. Contact your local agricultural extension service to see what is available in your area.
The larvae of the Hickory Shuckworm, Conotrachelus hicoriae, overwinter on pecan shells on the ground or tree. Moths emerge in the middle of May. First-generation moths deposit their eggs on pecan foliage; most moths die before pecan nuts set. In mid-July, dark-gray to reddish female moths use their long beaks to make a crescent-shaped puncture in the shell of an immature nut and drop one egg inside. These second generation larvae feed on the interiors of the nuts until the shells harden in mid-August. The nuts that drop often have chalky white deposit, scales the females left to seal the shell and protect the larva. The larvae inside the fallen nuts feed for about two weeks, then they exit through the hole and return to the soil. Horticulturalists at North Carolina State University recommend pesticides containing carbaryl, chlorpyrifos, dimethoate, imidacloprid and malathion.
Eggs of the Pecan Phylloxera, Phylloxera devastratrix, spend the winter inside the dead body of the female lying in protected places in a pecan tree. When the buds break in the spring, the eggs hatch and the insects, which resemble aphids and that are called stem mothers, feed on buds or growing leaves. Galls develop around the stem mother; she matures, lays eggs and dies. The eggs hatch; the nymphs feed inside the gall. The galls split open in July and the nymphs emerge as asexual, winged adults. These adults lay eggs in two sizes: small eggs hatch into males; larger eggs hatch into females. These mate to produce the overwintering egg. The females die, and their bodies protect the fertilized egg until spring. Insecticides labeled by the EPA for controlling pecan phylloxera include those with the active ingredients of lime-sulfur, carbaryl,and malathion.
Black Pecan Aphid
The eggs of the pear-shaped Black Pecan Aphid, Melanocallis caryaefoliae, spend the winter on the branches of the pecan tree. The aphid injects a toxin into the bottoms of pecan leaves, turning the tissue between the veins bright yellow. The damage turns brown and the leaves can drop, reducing the production of nuts. Horticulturalists at the University of California Davis campus recommend treating with insecticides containing Dimethoate E267, Imidacloprid or Chlorpyrofos.