University of Minnesota Extension — Wasps seem to be a buzz-word among grape growers this week, between the viticulture Facebook groups and recent emailed questions.
Wasps are not only a nuisance and safety hazard during harvest. They also feed on ripe fruit, leading to bunch rots and unusable clusters. Once berries are spilling juice, they attract fruit flies and sour rot, requiring further sprays and further costs.
The Dilemma of Managing Wasps
Often the first question people ask about wasps is “What can I spray for them?” But spraying for wasps is not the only way to manage them.
In fact, there are no insecticides labeled for social wasps in vineyards, according to UW-Madison. Since the label is the law, one cannot legally recommend spraying your vineyard with insecticides to kill wasps.
However, several insecticides growers spray for multi-colored Asian lady beetles and spotted wing drosophila might also kill wasps in the process, and I get into that at the end of this article.
Destroying Nests and Trapping Wasps
First, I want to talk about destroying wasp nests and trapping wasps to get them out of the vineyard. This is a legal method and can prevent populations from building up in the first place.
Tom Plocher has successfully reduced the yellowjacket population in his vineyard with this two-pronged approach. Within a day of setting up the traps, he had caught hundreds of wasps and noticed a significant reduction in wasp activity in the vineyard.
Plocher sets up plastic traps at the end of every row for a “trap and kill” method. Inside the traps, he uses a bait of:
- 2 parts water
- 2 parts apple juice
- 2 parts apple cider vinegar
- 1/2 part sugar
- A few drops of dish soap after adding the bait
He says that the wasp traps are available with 2-day delivery on Amazon.
In hot weather, he refills the traps every 2-3 days and after a heavy rain. He says that “It’s a pain to do this. But when I got the traps going out there, the yellowjackets vacated the grapes.”
While you wait for the traps to be delivered, try to locate the wasp nests and destroy them:
- In locating nests, it’s beneficial to understand what type of wasps you have and how they nest. This article is helpful. Only kill wasps if necessary, because they can actually be helpful at reducing populations of other insect pests. In other words, try to be sure you’re targeting the right nests.
- “Yellowjackets” refers to a group of wasp species that includes both ground-nesters and aerial-nesters
- Look for wasps flocking to burrows in the ground, to identify ground nests.
- To find aerial nests, look for brown “paper nests” on the sides of buildings.
- Use extreme caution when attempting to destroy nests, including protective face coverings, eyewear, and clothing; the article linked above says that aerial nesting yellowjackets can be particularly defensive of their nests.
- Use a wasp spray containing effective active ingredients. Wasp sprays are widely available at hardware stores and garden centers.
Plocher was able to locate a nest near his vineyard and safely destroy the wasps inside.
He says, “I also got the nest under control. I went out at 5 AM when the wasps were not active yet, shot foamy wasp spray down into the tunnel and blocked the opening with a big rock. Checked it yesterday and there was no activity around it.”
As mentioned at the beginning, there are no insecticides labeled for social wasps in vineyards; therefore, I cannot legally recommend spraying your vineyard specifically for wasps.
However, in the process of spraying insecticides for spotted wing drosophila (SWD) or multi-colored Asian lady beetles (MALB; a common harvest-time insect pest), growers may also end up killing wasps depending on what product is used. Please refer to this article from University of Wisconsin-Madison Extension Fruit News for a list of insecticides and their relative efficacy on wasps, MALB, and SWD: https://fruit.wisc.edu/2020/09/03/scouting-report-wasps-are-picking-up/ — By Annie Klodd, Extension Educator, Fruit & Vegetable Production, University of Minnesota Extension