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Thursday, August 5, 2010

What to Watch For - Wasps and bees in grapes

Wasps and bumble bees feeding on grapes. Photos: Ric Bessin, University of Kentucky Entomology

Today I had 2 phone calls and emails about wasps and bees feeding on grapes. Given our warm summer, this is not a surprise. In fact, last Friday when Turner Sutton, NCSU Plant Pathologist, and I were visiting vineyards last week we noticed several varieties (Marsanne & Viognier, to name a few) that were nearing harvest. Like many other crops, this is about 2 weeks earlier than normal. I said to Turner as we were leaving, "All this ripe fruit says to me is that I need to be ready for calls about bees, wasps, and green June beetles," and here we are!

Ripe or nearly ripe fruit coupled with the rain we have recently gotten is a recipe for splitting and other mechanical injury. These injured fruit will attract bees, wasps, and beetles, but they will not just feed on the damaged fruit. Once these opportunist insects are in the grapes, they can also feed on relatively sound fruit.

As I told both people I spoke with today, I do NOT advocate treating bees and wasps with insecticide. There are several reasons for this, with the foremost being that these are beneficial insects. They are our pollinators and predators that we work so hard to maintain all other times of the year. Pollinator heath is a major issue across agriculture systems, and is it irresponsible to be treating bees and wasps with insecticides in grapes. Even if pesticides were used, they will not solve the problem. Most bees and wasps are social insects with large colonies including foraging workers and reproductives. Only a fraction of the workers from a colony will be present in grapes at any given time, and no pesticide applied during harvest is going to have a long contact residual. This means that a pesticide application will kill the relatively small number of foraging workers in a field when it is applied, but leave the rest of the colony intact to re infest when the pesticide has dissipated.

What can be done to reduce bee and wasp injury?

Be ready to harvest.
I am not advocating harvesting fruit before you reach desired brix, but if fruit is ripe enough to split and attract bees and wasps, it is not far from harvest-ready. Harvest clusters as they become mature. This may mean picking several times and picking the early ripening areas (ie. the sunny side of the row) first.

Practice good sanitation.
Remove damaged fruit from the field promptly. Fruit left on the ground or on the vine will attract insects. Powdery mildew and thrips damaged fruit are more prone to splitting.

Be choosy about what you harvest.
Not all the grapes in the field will make it to the crusher. If wasps and bees are damaging a few early ripening clusters, remove them from the field preharvest. Do not harvest damaged fruit.

Consider trapping.
Several traps are marketed for wasps. Providing an attractive lure outside your planting may reduce populations in the vineyard. Suggested lures include soda, sugar syrup, and meat. Yellow trap are typically the most attractive.

Check the field for nests.
Wasps in particular can make nests on trellis wires or vines. If there are nests present in fields, these can be spot treated with insecticides or removed. Surrounding areas should also be scouted for nests, which can be spot treated.

Protect yourself.
Wear gloves, and if necessary, a head net when harvesting.

Ripening fruit at Junius Lindsay Vineyard. Photo: HJB

The early season means we need to be prepared for more wasp and bee presence as ripe fruit develops, but this are not unmanageable issues. Happy harvesting!

More information
Harvest pests of grapes - University of Kentucky

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