Study identifies least-toxic insecticide for controlling vine mealybugs in grapes
UC researchers have conducted studies on six insecticides to determine which provide the most effective control against vine mealybug in grapes while causing the least harm to beneficial insects. In addition to studying the insecticides’ compatibility with a biological control program against this pest, the research team also investigated vine mealybug resistance to these pesticides.
Damage by vine mealybug impacts wine, table, and raisin grapes, which combined represent a $2.3 billion crop grown on more than 790,000 acres throughout California. A black, sooty mold often grows on the honeydew this pest secretes, making the grapes unfit for consumption.
“The insect infests plant roots and feeds beneath the bark, making them difficult to detect,” said Walt Bentley, UC IPM advisor and project co-leader. “They’re also difficult targets for foliar insecticides and in many cases are protected from natural enemies by remaining in inaccessible locations on the grapevine.”
Scientists tested the insecticides’ toxicity to one parasitoid, Anagyrus pseudococci, and two species of predators, Cryptoleamus montrouzieri and Hippodamia convergens.
Spirotetramat (Movento), a new insecticide, was the least toxic to all three species of beneficial insects while chlorpyrifos (Lorsban) was the most toxic against all stages of vine mealybug. Spirotetramat also was effective against all immature stages of the vine mealybug although less so against adult females. Toxicity to natural enemies was intermediate for the four remaining insecticides—imidacloprid (Admire), buprofezin (Applaud), dimethoate, and methomyl (Lannate).
Although research shows imidacloprid is quite toxic, it was less so against early stages of the pest. Buprofezin activity was stage-specific and proved to be especially potent against the first instar larval stage. Dimethoate and methomyl were variably effective against vine mealybug.
The tests also showed no sign of vine mealybug resistance to the pesticides.
“The information provides some basics not only on pest susceptibility but on how to put the insecticide puzzle pieces together to provide pest control, prolong the use of the products, and promote biological control,” Bentley said.
Entomologists Thomas Perring and Nilima Prabhaker of UC Riverside also provided project leadership.
Funding for the project was made possible from Viticulture Consortium West through Unified Grant Management for Viticulture and Enology.
Walt Bentley, (559) 646-6527
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