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Keep eye out for destructive pests at fall pecan harvest

During the fall pecan harvest, growers should keep an eye out for two hungry, destructive pests that have the potential to seriously affect pecan yields: the pecan weevil and pecan nut casebearer.

“The pecan weevil is one of the most severe pests for pecan trees in North America,” said Carol Sutherland, an entomologist with New Mexico State University's Cooperative Extension Service. In New Mexico, we've had infested orchards and trees in Dona Ana, Otero and Luna counties.

“The pecan industry in New Mexico is supporting an aggressive program to prevent the weevil from becoming established.”

Adult pecan weevils have a plump, grayish-brown body with wings and are close to half an inch in length. The insects are distinguished by having extremely long, thin snouts and can easily blend into the bark of pecan trees.

Because weevils may stay in the nuts long after harvest, Sutherland said, growers should inspect their pecans carefully both before and after harvest to prevent the spread of the insect.

“The easiest thing to look for now that nuts are beginning to ripen are small round holes, about the diameter of a pencil lead in the shell of the nut,” Sutherland said. Pecan weevils chew their way into pecans, leaving perfectly round holes. If you were to crack open such a nut, you would find a c-shaped, creamy white grub on the inside, and these grubs will chew up the interior of the nut meat to the point that there's nothing left.”

The pecan nut casebearer, another destructive pest, has been found in southern New Mexico since the early 1990s, and has occupied parts of the Mesilla Valley. The pecan casebearer is a moth, but it does not become destructive until it produces a caterpillar.

“When pecan nuts are fairly small, the caterpillars will feed voraciously first in one nut in a cluster, and then move on until all of the nuts in a cluster are hollowed out,” Sutherland said. “Growers should look for signs of the pecan casebearer year round, because damage will increase as the insect becomes established.”

The pecan casebearer moth is small and grayish-brown, with a fringe of tall, thick scales running along the base of the wings. The off-white to grayish color caterpillar is about half an inch long. Signs of the pecan casebearer are small, irregular holes in the nut shell and tiny white eggs inside developing nuts.

Treatments to prevent pecan casebearer infestation can be applied in the early summer. Growers who find signs of the pecan weevil or casebearer should contact the county Extension offices.

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