Western grapeleaf skeletonizer control in grapes with reduced-risk insecticides

COLLABORATORS:  Walt Bentley, IPM Advisor; and Farm Advisors Carmen Gispert, Jennifer Hashim, and Steve Vasquez.

Western grapeleaf skeletonizer is a pest of grapes that periodically defoliates vineyards.  Granulosis virus, which has historically controlled this pest, has been less effective than in previous years.  This has been true in Kern, Fresno, and San Diego counties.  The primary objective of this project was to re-evaluate how skeletonizer is managed in grapes.  The backbone of this objective was research on the effectiveness of several new reduced-risk insecticides that have been registered in grapes during the past decade.

The data showed that three of the newer reduced-risk insecticides (Success, Assail and Provado) are all highly effective as knock-down products for skeletonizer (regardless of the size of the larvae) compared to grower standard treatments cryocide and Bt that only did well against small larvae.  This is

significant because it means that a PCA can wait for a longer period of time to see if the virus will present itself and provide control. In many cases, waiting a little longer will allow the virus to provide control; and in the case that it doesn't, one of these newer insecticides can be used.  It may also be possible in certain cases to piggyback skeletonizer control while using these other insecticides of other pests like leafhoppers and sharpshooters (Assail or Provado), or thrips or other species of worms (Success).

Websites

• UCIPM Pest Management Guidelines: Grape