It looked like candy at first, stuck onto the tendrils of wild fox grape. But in fact it’s grape blister gall. Definitely a new one for me.
Several species of small flies, or midges, are known to cause galls on grape vines. There are three types commonly found in the Midwest: the Grape Tomato Gall, the Grape Blister Gall, and Grape Tube Gallmaker. These all belong to the Diptera: Cecidomyiidae family. Blister galls and tube galls seem most common on wild and cultivated grapes… in Indiana.
The adult midges lay their eggs either on or in the leaves, leaf petioles, tendrils, or cluster stems. Orange, maggot-like larvae hatch from the eggs and enter the vine tissue. Fleshy or blister type galls, depending on the species of fly, are formed by the plant when the larvae begin to feed. Blister galls are usually red or green and form on both shoots and leaves (Figure 1). Tube galls usually form on leaves only (Figure 2). Fully developed larvae exit the gall through small holes (Figure 3) and drop to the soil where they pupate. Some species may produce up to three generations per year.
These galls do not usually inflict economic injury to the vine and no control measures are recommended. Removing the galls may be of some benefit in reducing the numbers of flies present in the vineyard. Removal should occur before small holes are seen in the galls (Figure 2), as this indicates that the larvae have already emerged.
Williams, R., D. Pavuk, and W. Rings. 1986. Insect and Mite Pests of Grapes in Ohio. Ohio State University Extension Bulletin 730, Research Bulletin 1179.
Isaacs, R., A. Schilder, T. Zabadal, and T. Weigle. 2003. A Pocket Guide to Grape IPM Scouting in the North Central and Eastern U.S.. Michigan State University Extension Bulletin E-2889
Clark, L. and T. Dennehy. 1989. Grape Tumid Gallmaker. New York State IPM Program. Cornell University fact sheet.