In the previous issue of this newsletter, we mentioned seeing up to 18% shoots damaged by grape plume moth caterpillars at the West Madison Agricultural Research Station (WMARS). These have all pupated by now and, since there is only one generation per year in Wisconsin, will no longer be found in the vineyard this year. More information about grape plume moth can be found in issue 5 of the newsletter last year.

However, in addition to grape plume moth, there are other species of leaf rollers in Wisconsin vineyards, which continue to feed throughout the summer. These species all pose very little economic threat, aside from occasional localized damage, and can be present at relatively high levels (up to 20% of shoots affected) before an insecticide application is recommended. Although these grape leaf rollers are rarely present at economically damaging levels, it can be helpful to learn to identify them, and to monitor for them and predict their life cycle in your vineyard.

At WMARS in early June, we found a single shoot with two Grape Epimenis caterpillars. Grape epimenis leaf-rolls are similar to those of the grape plume moth, but, after opening up the leaf, the caterpillars are black and white striped with distinctive red/brown head capsules. Grape epimenis can generally be found at low densities in most Wisconsin vineyards, but does not reach economically concerning levels.

The Eight-spotted forester caterpillar is related to, and somewhat similar in appearance to, the grape epimenis. However, eight-spotted forester has more distinct coloration, with yellow, white and black stripes. These caterpillars are not leaf-rollers, but feed on and skeletonize the foliage, and may show some leaf webbing as they feed. The first generation appears around bloom and pupates in mid-summer; another generation may feed on grape leaves in the late summer and fall. These show population fluctuations, and in some locations may reach high numbers some years, but are rarely problematic for consecutive years and very rarely require control measures.

The grape leaf folder folds the grape leaf so that upper surface of the leaf is enclosed, and feeds on the edges of the leaf within the protected fold. The caterpillar is a light green in color, and each will fold and damage two or more leaves during its development. This insect also has two generations per year, with the second generation causing the most foliar damage.

Another foliar feeder you may see in the vineyard this time of year are larvae of the grape flea beetle. These small, dark larvae make uneven holes between the veins of the grape leaves. Similarly to the leaf-roller caterpillars, grape flea beetle larvae rarely cause economically significant damage. However, the adults of this species can be quite damaging to grape buds in the spring, so a large number of flea beetle larvae can indicate a potential problem with the adults the following spring. More information about grape flea beetle adults and control was provided in the WI Fruit News, volume 2 issue 2. A great resource to learn more about grape foliar feeders is the Ohio State University extension bulletin: Insect and mite pests of grapes in Ohio by Williams, Roger, Pavuk, Daniel, and Rings, Roy (1986).

This article was posted in Grapes, Insects and tagged GRAPE EPIMENIS CATERPILLAR, Grape Flea Beetle.