Harvest is now underway in some locations for some cultivars and there are a number of insects that you should think about as they can become problematic at harvest. These include social wasps, multicolored Asian lady beetle (MALB), and drosophila flies.

Social wasps are picking up in the vineyard blocks at the West Madison Agricultural Research Station (WMARS) and at several commercial vineyards. These may include yellow jackets (Fig 1), bald-faced hornet (Fig 2), and paper wasps (Fig 3). Social wasps can be a problem when feeding on grape clusters and can become a nuisance at harvest when they come into contact with grape workers.

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At this time of the year, social wasps (and honey bees) are attracted to sugar sources and ripening and ripe fruits can provide such resources for them. The bald-faced hornet (Fig 2) initially feeds on already damaged fruits and, after getting a taste for them, proceeds to attacking sound fruit. Others species, such as the German yellow jacket, can feed on damaged fruit and can also cause the initial wound on sound fruit to a lesser extent.

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, such as Delegate, Entrust, and Mustang Maxx should provide adequate control for wasps (Table 1).

MALB (Fig 4) are also showing up in grape as they are attracted to sugar sources to stock up on for the winter. While MALB have not been shown to cause the initial damage to grape berries, they can be hiding in clusters and harvested with the grapes. Ladybugs harbor a bitter chemical (2-isopropyl-3-methoxypyrazine) in their hemolymph that taints the resulting wine when lady bug are crushed with the grapes. The thresholds for lady bug taint are: 1.3 MALB per kg of red grapes and 1.5 MALB per kg of white grapes. The suggested action threshold is 0.05 – 0.6 MALB per cluster. Yellow sticky cards can be used to monitor populations and should be set up 4 weeks prior to harvest, with 4-6 yellow cards per acre. Cultural control practices include shaking clusters at harvest to dislodge MALBs, covering harvest bins where clusters are stored, floating clusters in buckets of water, and vacuuming beetles off of the grapes.  Several short pre-harvest interval insecticides are available to manage MALB (Table 1).

Drosophila flies are pretty much ubiquitous and feed and lay eggs in damaged grapes from the moment they ripen until harvest is completed. While our research has shown that in all wine grape cultivars tested, spotted-wing drosophila (SWD) was not able to damage intact grapes, they can still lay eggs in cracked grapes. Drosophila flies have been shown to vector the pathogens responsible for sour rot and managing drosophila flies with short pre-harvest insecticides (Table 1) around harvest can reduce the incidence of sour rot. For more detailed information on the sour rot and drosophila interaction please refer to this webinar: “Managing grape bunch rots”. If you find drosophila flies around your grapes but no sour rot, we recommend monitoring for larvae inside the fruit by crushing a handful of berries in salt water (4 cups of water and ¼ cup salt and leave for 1 hr) and apply insecticides if you find larvae inside the fruit. 

As you are 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.

For more detailed information on managing these insects, you can watch this webinar “What to do now in the vineyard: veraison to harvest”.

Happy harvest!

This article was posted in Insects and tagged Christelle Guédot, drosophila flies, Grapes, Harvest, insects, MALB, multicolored Asian lady beetle, social wasps.