Lorraine Berkett & Morgan Cromwell, University of Vermont
Rose chafer (Macrodactylus subspinosus Fabricius) adults emerge at bloom and immediately attack grape blossoms and skeletonize leaves, eating all the tissue around large veins. They can cause extensive damage to foliage and completely destroy blossom buds and/or developing berries, resulting in reduced grape yields. Damage can be severe in vineyards with sandy soils, the preferred habitat for these beetles.
Physical removal and destruction of this insect pest can manage the population when only a few beetles are present; however, when greater than two beetles per vine are seen during vineyard monitoring, a chemical spray is recommended. Intensive baited trapping of the beetles over multiple years has shown to reduce populations to below threshold levels. An insecticide application in addition to trapping may be needed when populations are high. Chemical applications should continue through the first or second post-bloom spray when pressure is severe. Refer to a grape pest management guide (see Recommended Links) for insecticide specifics and efficacies. Cultivation between rows to destroy the larvae may reduce the population but will not provide sufficient control of the pest. Rose chafers contain a toxin that can be deadly to birds (including chickens) and small animals if the beetle is ingested.
The rose chafer is a light tan beetle with a dark brown head, about 12 mm (½ inch) long and has one generation a year. Larvae (C-shaped grubs) overwinter underground in the soil. They move closer to the surface and begin to feed on grass roots until they pupate in the spring. Adults emerge during late May or June in most areas, around grape bloom, and congregate on plants to mate and feed. The females lay eggs just below the ground surface. They prefer grassy areas of sandy, well-drained soil. The adults live for three to four weeks after emergence. The eggs hatch into small, white grub-like larvae, which feed on roots of grass, weeds, grains, and other plants throughout the summer. They move down in the soil as the temperatures decline, where they will overwinter until the next growing season.
Rose Chafer, Michigan State University
Rose Chafer, Ohio State University
Rose Chafers, University of Minnesota
Field Guide for Integrated Pest Management in Pacific Northwest Vineyards. Washington State University
Reviewed by Eric Stafne, Mississippi State University and Elina Coneva, Auburn University