As we are begin to see veraison on some grape varieties, social wasps are starting to show up at some vineyards we visited last week. Social wasps may include yellow jackets (Figure 1), bald faced hornet (Figure 2), and paper wasps (Figure 3). These wasps can be a problem when feeding on grape clusters as well as a nuisance at harvest when they come into contact with grape workers.
As we approach harvest social wasps are more and more attracted to sugar sources that ripening and ripe fruits can provide to them. Some wasps initially feed on already damaged fruits and, after learning to feed on damaged fruit, proceed by attacking undamaged fruit (such as the bald-faced hornet, Dolichovespula maculata; Fig 2). Others may attack damaged fruit as well as sound fruit (such as the German yellow jacket, Vespula germanica) but to a lesser extent than on damaged fruit.
Managing social wasps in fruit crops can be challenging. Removing overripe and damaged grapes can help reduce the buildup of wasp populations around harvest time. Once wasps are present, insecticides with short pre-harvest intervals may be applied. However, there is no product labeled specifically for social wasps and the regional spray guides do not provide any options for wasp control. Products with short pre-harvest intervals, such as Delegate, Entrust, and Mustang Maxx should provide adequate control for wasps.
Happy harvest!This article was posted in Insects and tagged bald-faced hornets, Christelle Guédot, Grapes, insects, paper wasps, Wasps, yellow jackets.