Wasps, hornets, and even bees are opportunistic feeders, and during the mid to late summer they are actively searching for sources of sugars. Once they find sources of sugary foods, they will aggressively forage in those areas and recruit additional workers from the colony. As such, these stinging insects can be a real nuisance in grapes, especially at harvest. Unfortunately, there are no labeled insecticides to be used against wasps in vineyards, and it is technically illegal to spray anything to kill bees.
The most effective way of managing wasps/hornets/bees in the vineyard is to manage the crop to reduce injury that attracts the insects. While wasps, like yellow jackets, can feed directly on sound grape berries, they are usually attracted initially to damaged fruit – meaning healthy grapes are less susceptible. This can be done by minimizing injury caused by birds, other insects and diseases. Also, removing overripe and already damaged fruit from the grapevines can eliminate attractive sources.
At harvest, it is unfortunately usually too late to reduce damage and focus on grape berry health, so obviously we need alternative options. Since there are no labeled insecticides for wasps in the vineyard, one thing you can do is manage wasp nests on the vineyard exterior. Locate and manage wasp nests near vineyard (eg. on buildings, dead trees). You can use standard wasp sprays to control nests around the vineyard, or trap wasp adults with commercial or homemade traps.
Admittedly, tracking down nests is difficult and trapping won’t work for all species of wasps, but chemically managing other late-season insect pests may also help suppress stinging pests as well. For example, using Mustang Maxx (zeta-cypermethrin) to manage spotted wing drosophila also has efficacy against wasps and has a 3-day pre-harvest interval (PHI). Similarly, Delegate (spinetoram) or Entrust (spinosad), which are also labeled for spotted wing, have efficacy against wasps, but have a 7-day PHI. If you plan to use any insecticides, be very mindful of the preharvest restrictions and be sure to use all appropriate safety equipment.
We don’t have a ton of options for wasps/bees, but hopefully one of the mentioned options will help protect your vineyard visitors and pickers from these nuisance pests – Brett Blaauw, Entomology Extension Specialist, University of Georgia.