We have been operating under the assumption that no bait yet invented by man for use in yellow jacket (YJ) traps had the necessary allure to distract a YJ from a nice ripe grape. But if the bait and traps are inexpensive enough (like free) to cover a large vineyard, and they are installed shortly after veraison, the chances of substantial YJ population reduction may continue through harvest.
The idea for a homemade trap comes from an unknown German vineyard manager/vintner and was passed on to us by John Hall, a Pinot Noir grower in the vicinity of Traverse City, Michigan.
Plastic soda bottles (personal size) with the tops removed are tied to trellis, or bird net, throughout the vineyard. Each bottle contains 1 to 1.5 inches of a wine and vinegar mixture (proportions not specified). John reports good results with these traps at harvest time. The traps should be available to the YJ's while the grapes are ripening. This means they should be installed right after veraison.
Whether the YJ's are too dumb to find the top of the bottle they entered through, or the wine/vinegar bait has a toxic, and/or anesthetizing capability is unclear. We also don't know how these traps will work with larger stingers such as wasps and hornets. John reports no problem with these critters in his vineyard. If anyone has experience with the open-top bottle trap and the YJ's larger cousins, please give us a report.
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