Rose chafer populations are very high

A high population of rose chafers in some areas of the state can do serious damage to Christmas trees and ornamental plants.

The rose chafer, Macrodactylus subspinosus, is now appearing in large numbers in many areas of northern Michigan. The rose chafer, commonly known as scarabs, is a native insect and a member of the same family as June beetles. However, the adult rose chafer looks quite different from a June beetle. Adults are about 0.05 inches long, slender, usually light tan with long, reddish-brown legs. They are rather gangly in appearance. They are often found in mating pairs and fly during daylight hours and are not attracted to lights at night like June beetles. Adults contain a distasteful chemical; few birds can eat them without being sickened. The grub stage is typical of the entire family – a soft bodied, “C”-shaped white grub with six legs and a prominent brown head. There is a single generation per year with the adults showing up in June. The activity of adults typically lasts for only two to three weeks.

rose chafers
Rose chafers feeding on Rugosa Rose. Photo credit: Duke Elser, MSUE

This year we are finding adult rose chafers causing significant injury to Scotch pine, spruce, Fraser fir and other ornamental plants. Adult rose chafers feed on the foliage, buds, flowers and fruits of hundreds of plants. They have weak jaws, so they typically eat only the tenderest portions of leaves, resulting in irregular holes on new needles or leaves, damage to tender stems or broken, green to brown needles. Growers may also notice the period of adult flight lasts only a few weeks and should be done by the end of June. They are good fliers and are capable of traveling great distances to find a meal.

rose chafers
Rose chafers on Scotch.

rose chafers
Broken, green or brown needles from feeding by rose chafers.

The grub stage of the rose chafer feeds on plant roots, but they are typically found only in sandy, open areas where wild grasses and weedy plants predominate. The grubs of rose chafers are not pests of lawn grasses and landscape plants like their June beetle cousins.

In most years, adult rose chafers are moderately annoying. In high population years like this year, they can be serious pests of Christmas trees, ornamentals and other crop plants, requiring pesticide sprays to protect plants from the voracious adults. Sprays may have to be applied frequently in order to protect plants from injury as it only takes a short time for a lot of feeding injury to occur when the adult population is high.

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