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Managing Mites in Long Island Vineyards

Release of biological control agent provides new understanding of biological control of spider mites

Spider mites, especially the European red mite, can greatly reduce grape yields by feeding on grape leaves. Last year two Long Island vineyards were "inoculated" with tiny biological control organisms (the predator mite species T. pyri) in an attempt to manage the spider mite problem. This method is cheaper, more reliable, and more sustainable than chemical management. Furthermore, pesticide use is highly regulated on Long Island and spider mites develop resistance to pesticides very quickly.

Because it was thought that T. pyri cannot be found in Long Island, apple clusters harboring predator mites were shipped there from Geneva, New York, and were literally tied onto grape vines in 1996. The importation method was an immediate success. The T. pyri set to work controlling the European red mite (ERM) problem in their new homes.

The question of the hour in the 1997 growing season was: how is T. pyri faring over the long haul? Is it surviving the winter and reproducing? Is it compatible with pesticides used in vineyards to manage plant diseases? Monitoring, measuring, and comparing in four vineyards--including two additional ones in which T. pyri was introduced for the first time in 1997--resulted in these findings:

Biological control of ERM is being achieved. There were no ERM in any of the samples from T. pyri-release plots in 1996. In contrast, ERM densities rose as high as 50 per leaf in one non-release plot.
Numbers of T. pyri steadily declined over the July to September sampling period in the plots inoculated with the predator mites in 1996 and either declined or remained constant over the same period in the 1997 release sites. This suggests that pesticides do have an adverse effect on them.

One unexpected, positive turn of events was the discovery of T. pyri in some of the plots in which none were released. Because of their low dispersal tendency, it is very unlikely that they moved there from the release plots. A more likely explanation is that T. pyri is, after all, native to Long Island. This can only help in the goal of obtaining biological control of ERM throughout the region.