Sep 27, 2021

Wasps are picking up in Wisconsin vineyards

As we are approaching harvest, there are a number of insects that you should prepare for as they can become problematic at harvest.

These include multicolored Asian lady beetle (MALB), social wasps, and spotted-wing drosophila (SWD), which were all discussed during our last grape webinar of the season that you can watch here: “What to do now in the vineyard: veraison to harvest”.

Social wasps have been picking up inthe vineyard blocks at the West Madison Agricultural Research Station (WMARS). These include yellow jackets (Figure 1), bald faced hornet (Figure 2), and paper wasps. Social 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.

Social wasps, at this time of the year, are attracted to sugar sources and ripening and ripe fruit crops can provide such resources for 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 but to a lesser extent (such as the German yellow jacket, Vespula germanica).

Managing social wasps in fruit crops might 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 with wasps on its label 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.

Looking at insecticides to manage harvest insects, you can refer to the table below that shows pre-harvest intervals and efficacy for multicolored Asian lady beetle (MALB), social wasps (Wasp), and spotted-wing drosophila (SWD). We do not endorse a product over others and please check the label before using any pesticide.

Table 1. Selected insecticides and active ingredients, pre-harvest intervals (PHI), and efficacy on multicolored Asian lady beetle (MALB), social wasps, and spotted-wing drosophila (SWD). G: Good, E: Excellent, P: Poor, -: no information available.

Thanks to Beth Workmaster for scouting at WMARS.

– Christelle Guédot, University of Wisconsin 

Figure 1 at top. Yellow jacket, Vespula maculifrons feeding on split berries. Photo: Andi Nelson/UW-Madison