Learn how to effectively control pecan weevils using organic methods.
A serious late season pest of pecan and hickory trees, the pecan weevil (Curculio caryae) chews holes through the shuck and shell of nuts and are responsible for two kinds of damage.
The first type of damage is caused by adult weevils feeding on kernels prior to the shells hardening. Nuts punctured by weevils during this stage have a tobacco-juice-like stain around the feeding site. Damaged nuts often shrivel, turn black inside, and drop prematurely.
The second type of damage occurs later in the growing season when females place eggs within the newly formed kernels. After the eggs hatch larvae feed and cause further damage. These nuts do not drop. The pecan weevil causes serious crop loses and are found wherever pecan and hickory trees are grown.
Adults are hard shelled beetles about 3/8 inch long, with long slender snouts (females have a snout longer than their bodies) and thin legs. They are reddish brown in color and densely covered with olive-brown hairs and scales. Larvae are fat, creamy white, C-shaped grubs. They have reddish-brown heads and grow to 1/3 inch long.
Adult weevils and larvae overwinter in the soil. Most adults emerge from the soil during August and the first week of September. When the nuts reach the dough stage of development, mated females lay 2-4 eggs in separate pockets within the kernels. After the eggs hatch, the legless larvae feed for about 35 days inside the nuts. Between late September and December larvae exit the nuts through a small circular hole, drop to the ground and burrow into the soil to a depth of 4-12 inches. They spend one to two years in the soil before pupating in the fall. (Most of the grubs will pupate the following fall. Although some do not pupate until the fall of the next year.) The pupal stage last about three weeks. Adults remain in the soil until the following summer. There is one generation every 2-3 years.
Pecan Weevil Control
Use beneficial nematodes to attack pecan weevil larvae in the soil. Applications should be made under trees at least out to the drip line — or a little farther. Larval populations may also be reduced by killing the adults soon after they emerge from the soil, thus preventing egg laying in the nuts. Growers with only a few trees can place tarps under the canopy during August, especially several days after a rain, and jar the limbs to shake adults free. Weevils that fall will remain still for several minutes and can be collected and destroyed in a bucket of soapy water. This technique can be repeated until mid-September or until no weevils are found. Usually botanical insecticides are applied after 6 weevils are jarred from a single tree. Normally, three to five sprays, every 5-7 days are required.
Photo Credit: Clemson University