by Paul Schattenberg, Texas A&M AgriLife
The Texas A&M AgriLife Extension Service is seeking assistance in locating possible pecan weevil infestations in Bexar, Hays, Comal and Travis counties, said Dr. Larry Stein, AgriLife Extension horticulturist in Uvalde.
“The pecan weevil is a serious pest of pecan,” Stein said. “Previously, pecan weevil distribution was unknown in Texas until last year when they were found near the Wimberley area in Hays County. Most recently, we had a new pecan weevil identification in Comal County near the Guadalupe River. And there’s strong possibility of additional infestations within these and other nearby counties.”
Bill Ree, AgriLife Extension integrated pest management program specialist for pecans at the Texas A&M University Riverside campus in Bryan, said area landowners can help identify areas of infestation.
“Many of the areas within these counties are environmentally sensitive so that would likely preclude the use of chemical controls to help manage the weevil,” Ree said.
He said while there currently is no plan – or need – to quarantine affected areas, gathering information on the extent and range of the geographical distribution of this pest is important for educational purposes.
“If anyone finds a suspected infestation, pecans showing signs of that infestation can be taken to their local AgriLife Extension county office or can be mailed to me,” he said.
The address to mail samples for confirmation is: Bill Ree, P.O. Box 2150, Bryan, Texas 77806-2150.
Molly Keck, AgriLife Extension entomologist for Bexar County, said signs of pecan weevil infestation include seeing two to four legless white grubs inside the shell or small, round BB-shaped holes on the outside of the shell.
“The adult weevil is typically gray to brown in color and about 3/8 of an inch long,” Keck said. “The snout of the female is as long as its body while the male’s snout is a little shorter. The weevil larvae are cream colored with reddish heads and when grown can reach a length of ⅗ of an inch.”
She said adult weevils damage pecans by feeding on and/or laying eggs in them.
The key to weevil control is to prevent egg laying or oviposition, said Wizzie Brown, AgriLife Extension entomologist, Travis County.
Brown said because the pupae and adults are typically covered with several inches of soil and pesticides can’t get inside the nuts to attack the larvae, the only option is to manage infestations after the adults have emerged.
She said the best way to prevent weevils from laying eggs is to monitor pecan kernel development to determine when the earliest maturing cultivars might be susceptible to oviposition.
“Currently, the best way to manage pecan weevils is to avoid getting them,” she said. “This is achieved by spraying the tree with insecticide when the adults are on the tree laying eggs.”
She said pecan weevils can be controlled by spraying liquid applications of carbaryl, commonly sold under the brand name Sevin.
“You can kill weevils by spraying the trunk and lower scaffold limbs, but the best control is by spraying the whole tree at the right state of nut development,” she said.
Brown said to monitor adult pecan weevil emergence, landowners can set up insect traps near their pecan trees in late summer when the insect begins to emerge.
“The traps should be checked daily to monitor when the adults emerge from the soil,” she said. “Females will usually lay eggs four to six days after emergence, so the traps can be used to tell when the weevils are present as well as to get a general idea of the population numbers.”
She said if landowners choose not to use traps for monitoring, they can time insecticidal treatments for the pecan trees based upon when the pecan shell begins to harden.
“Female pecan weevils lay their eggs in pecans once shell hardening has begun, so it can be used as a method to time treatment,” she said. “The possible problem with this method is that it does not measure population levels of the weevils, so it may lead to unwarranted treatments.”