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NMSU Scientists Crack Down on Pecan Weevil

LAS CRUCES - New Mexican pecan growers should keep a sharp eye out for signs of a devastating bug known as the pecan weevil this winter, says a New Mexico State University researcher.

New Mexico State University entomologist Carol Sutherland points to a pecan weevil emergence hole. During the current harvesting season, NMSU scientists are looking for any signs of the devastating bugs, which destroy most nuts and contaminate the rest. New Mexico ranks in the top five of U.S. pecan producing states. (11/11/2002) (NMSU Agricultural Communications Photo by J. Victor Espinoza)

"Every effort should be made to find unreported infestations and eradicate them," said Carol Sutherland, an entomologist with NMSU's Cooperative Extension Service. "This is the worst pest for pecan nuts in the world. If you find either small round emergence holes or the grubs themselves, take the pecans to your county Extension office or to the NMSU Extension plant sciences department in Las Cruces for confirmation."

What makes this time of year so important is that harvesting brings all the nuts into one place at one time for cleaning, sorting and marketing, making it easier to perform a quick, yet through inspection, she said.

The top five states in total pecan production are Georgia, Texas, New Mexico, Arizona, and Louisiana, respectively. New Mexico produces up to $40 million worth of pecans in high-yielding years, and accounts for about 50 percent of Southwest production and 11 percent of the U.S. crop.

Now, as harvesting and processing begins, it's critical for everyone from those with one backyard tree to the largest commercial processors to look for this pest, so that it doesn't become established in New Mexico, Sutherland said.

Pecan weevils, which are native to North America, cut yields in several ways. Emerging adults feed on immature nuts in late summer, causing them to drop off the trees. Later in the season, females lay eggs in immature nuts that hatch into pecan weevil grubs. They burrow inside the nutmeats, destroying most nuts and contaminating the rest.

Pecan weevils were first discovered in New Mexico in the late 1960s in a small Tularosa pecan orchard and were quickly eradicated. After a 30-year absence, the pecan weevil once again resurfaced in Tularosa in 1998. Workers at an Otero County pecan cleaning plant noticed pecans with round holes about the diameter of a BB pellet, which are the pecan weevil's emergence holes. Creamy white, legless grubs with reddish-brown heads were also found inside pecans infested with pecan weevil larvae.

Since that initial discovery four years ago, the pecan weevil has been found two other times in New Mexico in sharply different settings: a commercial orchard near Vado in Doņa Ana County and some backyard pecan trees in Deming. In each case, affected areas were treated before the weevils could reproduce and monitored to prevent the pest from spreading.

"In none of these cases are we absolutely sure how the pecan weevils got there, but we do know they're living there," Sutherland said. "They didn't just fall off a passing truck."

Meanwhile, NMSU's Cooperative Extension Service, the New Mexico Department of Agriculture and the Western Pecan Growers Association continue to work with the region's producers to keep the weevil from becoming established in the state.

Pecan weevils are challenging to control because they spend much of their two- to three-year life cycle two feet underground, where treatments cannot reach, Sutherland said. Also, the large brown adults are very secretive when they emerge and any eggs or larvae are protected from insecticides by pecan nut tissues.

"It's a very tough, long-lasting problem to eradicate, and a potentially serious threat to the state's pecan industry," she said.