The Virginia PMG recommends using the Heterorhabditis or the Steinernema nematode. The nematode eggs hatch, and the young nematodes eat the host grub. These nematodes encounter the beetle grubs in the soil and lay eggs on the grubs.

However, a better option for organic control might be to treat the soil with parasitizing nematodes. What is a homeowner to do? At this time, Milky Spore is still recommended by the Virginia Pest Management Guide (PMG) as a control for Japanese beetles. Grubs under a flap of soil.No matter the mechanism of its demise, Milky Spore seems to have lost much of its punch. Or, perhaps, the Japanese beetles have gained immunity to Milky Spore over many generations effectiveness of many insecticides has been similarly degraded by insect mutations. It is possible, too, that the Milky Spore bacterium has evolved in a way that makes it less effective in controlling Japanese beetles. What happened? No one knows for sure, but speculation is that Japanese beetle grubs in the 1940s’ trials may have been weakened by environment stresses related to extremely high population levels. Recall that Milky Spore was thought to work at 90-to-95-percent control 60 years ago, implying that infectiveness was much higher than it is today. A Japanese beetle grub cannot be killed if it has not been infected. Infectiveness, a measure of how many insects in a population show signs of infection, dropped to about 39 to 44 percent in trials conducted in Kentucky. In recent years, scientists have attempted to reproduce the results of the 1940s with no success. Ever since, Milky Spore has been regarded as an effective control for Japanese beetles. It was credited with decreasing Japanese beetle populations by 90 to 95 percent. In the 1940s and 1950s, Milky Spore was used extensively in the East, particularly in Pennsylvania and Ohio. The beetles were then considered to be a serious invasive pest with no natural predators, a threat to food crops and ornamental plants alike. at the time, just 25 years or so after first appearing on this continent. Japanese beetles were running rampant in the eastern U.S. Milky Spore was isolated, developed and tested in the 1940s in a U.S. This strain of Milky Spore has no effect on other members of the Scarab beetle family, such as European chafers, that damage landscapes in some parts of the country.

Since it is a biological control, it leaves behind no harmful chemical residues.

Milky Spore has no effect on beneficial insects.

Its properties have made it a treatment of choice for these insects because: The strain that is commercially available to homeowners infects Japanese beetles and only Japanese beetles.

Milky Spore is the bacterium Paenibacillus popilliae. Recent field trials in Kentucky and Michigan have yielded disappointing results.

Control is achieved.īut extension scientists in several states are now questioning Milky Spore’s effectiveness. Over a multiyear timeframe, Milky Spore eventually kills off the grubs, which means they cannot develop into adults. The product is applied to the ground and gradually infects Japanese beetle grubs living there. Since the 1940s, homeowners have used Milky Spore to control Japanese beetles. By Gil Medeiros, Fairfax Master Gardener Intern

When to apply milky spore