Unwelcome companions of grape pickers are members of the wasp family Vespidae, Yellow Jackets. Picking grapes is much more enjoyable if you don't have to worry about being stung. Of course, there are likely to be several other varieties of wasp after your grape juice, but the Yellow Jacket seems to be the most pervasive, most persistent and most aggressive member of the group.
Early in the season, insect traps placed in the vineyard may capture a Yellow Jacket queen. If you accomplish this feat, you have substantially reduced the population of the pest in the vineyard area. How do you know if you have one? One morning you'll look in the trap and among the five or six dead Yellow Jackets floating in the bait will be an extra large one. You've got her! Her absence will make harvest much more enjoyable
This is a time sensitive operation. In mid spring, the queens quit circulating and get down to the business of raising obnoxious offspring. In addition to being lucky, your timing has to be right to use this method. Traps in the vineyard after bloom are not likely to trap a Yellow Jacket queen
The bait is a cup of fruit juice with a small piece of raw meat or fish floating in it. At harvest time, a little wine mixed with vinegar will get their attention faster. The insects enter the trap exhaust themselves trying to get out, fall into the bait and drown. That's all there is to it! During the entire process, the entrances are available as exits, but panic and other factors prevent the insects from finding them.
Thus far, we have not killed a valuable insect by placing these traps. The assortment of non-Yellow Jacket types we find in the juice are other wasps, hornets, gnats, flies and an occasional moth. The newer trap permits smaller moths to enter, and these may turn out to be grape berry moths, so that's fine. No honeybees have been victimized. However, if your neighbor is a beekeeper, proceed with caution and watch what you are catching and check with your local entomologist.
An 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 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. This was a surprise to us because we did not think any trap or bait would distract a YJ from a cluster of grapes. The traps are so cheap (free after teenager parties) that they can be installed throughout a large vineyard a few days after veraison and start the work of reducing the YJ population before the grapes are ripe.
Whether the YJ's are too dumb to find the top of the bottle they entered through, or the wine/vinegar bait has an anesthetizing capability is unclear. The big question is whether a Queen will let herself be caught by one of these traps. Results thus far in spring, 2000, are negative.
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