Green June beetles a menace to vineyards

Green June beetles have been feasting on wine grapes at some North Texas vineyards, and the insects’ unusually large numbers and appetite have hurt this season’s crop, experts said.

Traditional insecticides have helped, but researchers with the Texas AgriLife Extension Service are experimenting with traps as a method of managing the pests during the weeks prior to harvest, said Dr. Allen Knutson, entomologist with AgriLife Extension in Dallas.

“The beetle can be managed with insecticides, but because they appear just before fruit harvest, few insecticides can be safely used,” Knutson said.

The traps, however, show some early promise, he said.

Knutson and AgriLife Extension viticulturist Fran Pontasch in Stephenville started their project early this summer after growers suffered losses from green June beetles in 2008. They followed the plan for trapping the beetles from a researcher at the University of Arkansas who is working with them on this project.

“The traps capture a lot of beetles, but additional studies are needed to determine the benefit of mass trapping as a control method for green June beetles,” said Knutson, adding that he and Pontasch hope to continue the research next season.

About 70 test traps in total have been set around two vineyards, one near Springtown and the other near Bridgeport, Pontasch said. They’ve been baited with isopropyl alcohol, and they’re positioned to create a barrier around the vineyards to capture the hungry beetles before they reach ripening grapes.

The traps have captured as many as 600 beetles per week at their peak, she said. Still, some beetles were found feeding on grape clusters in the vineyards.

“Both of the study vineyards had to resort to using pesticides to prevent green June beetles from destroying their grape crops,” Pontasch said.

The beetles can be a nuisance in any given year, but this season these pests seem to be particularly abundant and damaging, Knutson said. It isn’t clear why their numbers were larger this year.

Pontasch said not all 90 North Texas vineyards have been raided by the beetles, but “we do know it’s widespread and destructive enough to be a problem.”

Estimates on the economic effects haven’t been determined, Pontasch said.

“Some are worse than others,” she said.

Not all the damage can be blamed on the beetle, as vineyards also suffered from spring frosts, Pontasch said.

The green June beetle, so named for its color and time of year it emerges, is robust and grows up to one inch long, Knutson said.

Strong fliers, the beetles lay their eggs in hayfields and pastures where the larvae feed on grass roots and organic matter, Knutson said. It has a one-year life cycle, feeding during the summer and laying dormant in the winter. The adult beetle can travel long distances for food. In addition to grapes, the beetles feed on peaches, blackberries and other soft-skinned fruit.

Though harmless to humans, the beetles can ravage grape clusters with 20 or more beetles feeding on a single cluster at a time, Knutson said.

“They attack just before the grapes are ripe,” he said. “They mass-attack grape clusters, ruining them by feeding on the fruit, contaminating the clusters and making them unfit for harvest.”

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