Several species of aphids infest pecans, including the black pecan aphid (Tinocallis caryaefoliae) and the yellow aphid (Monellia species). Aphids do little damage in small numbers. They are extremely prolific, however, and populations can rapidly build up to damaging numbers during the growing season. Damage occurs when the aphid sucks the juices from pecan leaves. The aphid is unable to digest fully all the sugar in the plant sap, and it excretes the excess in a fluid called honeydew, which often drops onto the leaves below. A sooty mold fungus may develop on the honeydew, causing the pecan leaves to appear black and dirty. Black pecan aphids cause the worst damage to pecans-they are responsible for the yellow-spotted dying leaves of many pecans in the Southeast.
Spray infested trees with an insecticide labeled for these pests, following label directions.
Laspeyresia caryana These worms, the larvae of small, dark gray moths, are also known as pecan shuckworms. They are pests of pecan and hickory trees wherever they are grown. The larvae spend the winter in shucks on the ground or in the tree. The shuckworms pupate and emerge as adult moths in the spring to lay their eggs on pecan leaves and nuts. The young larvae that hatch from these eggs tunnel into the soft green pecan shells and feed on the developing kernels. Infested nuts usually drop. Later in the season, after the nutshells have hardened, the larvae tunnel into the shucks. Their feeding damage interferes with the development of the kernels. Shuckworm damage may occur throughout the spring and summer.
Clean up and destroy all dropped nuts and shucks to eliminate many of the overwintering larvae.
Acrobasis nuxvorella These worms, the larvae of small, dark gray moths, damage pecans extensively. In spring the worms come out of hibernation when buds open, feed on the buds for a short time, then tunnel into new shoots to pupate. Adult moths emerge to lay their nuts on the pecans as they are forming. These second-generation worms make webs around clusters of nuts, boring into the pecans to feed and pupate. Each worm, before becoming a moth, eats three or four immature nuts, causing great harm. Damage lessens as nuts mature.
Destroy all infested nuts on the ground. Apply an insecticide labeled for this pest, following label directions.
Phylloxera species These insects, closely related to aphids, are common pests of pecan and hickory trees. Phylloxera eggs, laid in the fall, survive the winter on branches and twigs. The eggs hatch when leaf buds open in the spring. The emerging insects, called stem mothers, feed on new spring growth by sucking the plant sap. They inject a substance into the plant while feeding that causes the plant tissue to swell, forming galls. Eventually the galls envelop the feeding insects. After the stem mothers mature, they lay their eggs and die. When the second generation of winged insects matures, in late May or early June, the galls split open, releasing them. Although these pests are present throughout the summer, they are most damaging to new spring growth.
Once galls have formed, the insects cannot be killed. Appy an insecticide that''s labeled for these pests, following label directions.
Curculio caryae Both the immature and adult stages of this insect are very damaging to pecans and hickories. Adult weevils emerge from the soil in late summer and feed on immature pecans. The injured nuts drop from the tree. As soon as the kernels harden, female weevils drill holes through the shucks and shells and lay their eggs in the kernels. The grubs that hatch from these eggs feed on the kernels for several weeks, then chew a hole in the shell about 1/8 inch in diameter, leave the nut, drop to the ground, and burrow into the soil. They emerge as adult weevils after 2 to 3 years.
Weevils may also be partially controlled by shaking them from lightly infested trees. Place sheets under the tree, then lightly jar the limbs. Collect and kill the dislodged weevils that fall onto the sheet. Repeat every 3 or 4 days until the weevils are no longer present.
This plant disease, the most serious disease of pecans, is caused by a fungus (Cladosporium caryigenum). The fungus spends the winter on twigs, old leaves, and shucks on the tree and ground. In the spring, fungal spores are splashed and blown onto new growth. With adequate moisture, the spores infect the plant tissue, causing spotting and blighting. The infected tissue produces more spores, which spread to the young nuts. As pecan leaves mature, they become resistant to scab infection. The shucks are susceptible to fungal attack as long as they continue to grow and develop, however.
Remove and destroy old shucks and plant debris. Apply a fungicide labeled for this disease, following label directions.