Scouting at the West Madison Research Station (WMARS) vineyard occurred on 9/10/19 and there was no insect to report. No insecticide was applied on the WMARS grape vines since 8/21/19 and Japanese beetles are pretty much done for the season. No new grape phylloxera galls were observed, only old galls that remained on leaves that were not pruned out. Similar report from the Peninsular Ag Research station (PARS) in Door County, no JB or any other insect of importance to report.

Around harvest, it is important to pay attention to the presence of social wasps and multicolored Asian lady beetles (MALB). While early in the season, MALBs are beneficial insects that feed on aphids and other soft bodied insects, at harvest, they can become pests. MALBs come to the vineyards looking for sugar and feed mainly on areas of berries previously damaged due to other insects or diseases. The main concern with MALB is the fact that, if harvested with grape clusters, they may taint the flavor of the wine. MALBs emit a bitter defensive chemical compound when stressed and this compound affects the taste of the wine made from those berries. For more information on their basic biology, please refer to this previous article.

At this time, examine clusters closely for the presence of MALB adults. There is no economic threshold for MALB, because it depends on grape variety and what style of wine is being produced. The general recommendation is to apply a chemical control when an average of three or more adults is found per ten clusters.

To prevent MALB from infesting clusters in the first place, try to maintain healthy grapes, without any disease or insect damage which would provide access for the MALB. Once they are in the clusters, vigorously shake the clusters during harvest to dislodge the beetles. Of course, these methods may not always be manageable options. When chemical controls are necessary, some insecticides have shown good efficacy against MALB. It is especially important to take into consideration the pre-harvest interval when considering a spray program for MALB, since this is a pest that moves into the vineyard only shortly before harvest. As always, make sure to read the label before using any pesticide.

*IRAC Code = Insecticide Resistance Action Committee Mode of Action group

** Although these insecticides do not contain MALB on the label, they are registered for use on grape in Wisconsin, and have shown efficacy against MALB in insecticide trials.

Other insects to pay attention to at this time are social wasps. While none were observed in our scouting at WMARS or PARS, we are conducting experiments on wasps in vineyards and are observing similar species as in previous years, though they seem to be in lower numbers than previous years at the same time. While numbers are still fairly low at this time, they should only increase in the next few months. Few growers are starting to report wasps feeding on their grapes, however, many grape cultivars are still not fully ripe and wasps will continue to come in as grapes ripen. As with MALB, keeping grapes from being compromised by pathogens and other insects in the first place will help prevent high buildup of wasp populations. Once wasps are present, insecticides with short pre-harvest intervals may be applied. However, there is no product with wasps on the label and the regional spray guides do not provide any options for wasp control. The products mentioned in the table above for MALB are likely to have some efficacy against wasps, especially in the pyrethroids class.

Thanks to Andi Nelson and Annie Deutsch for scouting at the research stations.

Happy harvest!

This article was posted in Grapes, Insects and tagged MALB.