These buggers are primarily known for the lawn damage they cause, which seems especially noticeable on lawns with a thick thatch layer. Lawn sod with chewed- off roots, will roll- up like a carpet! If you have raccoons around, they may add to the damage by tearing up large areas of turfgrass to locate and eat these ‘C’ shaped morsels.
Let’s not get ahead of ourselves, since it’s the Japanese Beetle adults that are flying about now, stopping to dine on the foliage of various plants. We see them eating Geraniums in these photos, but according to my friend Sandy, Geraniums are actually poisonous to the Beetles, so it’s a very short meal. The soft ground, from frequent rainfall here in western Pennsylvania, will make things easier for the females, who back down into the sod to lay their eggs. If soil stays too moist, it can limit their successful re- population into the white, overwintering, C- shaped grubs seen in lawns.
As a quick review, the adult Japanese Beetle lays her eggs in mid- to late- summer. Those eggs become grub larvae that feed on the roots of plants and lawn grasses. As temperatures drop in winter, the grubs migrate lower into the soil profile, remaining there until the soil warms enough in Spring for them to return to the surface.
Most grub controls are focused on the initial ‘young grub’ stage since they are most vulnerable then. Lawn care companies generally begin applying grub control pesticides in the August- September time frame for that reason. Pesticide effectiveness is often reduced by inadequate rainfall or irrigation, and a thick thatch layer.
For those who prefer a more environmentally- friendly solution, the coming weeks should be a good time to apply “Milky Spore Powder” which is known as a “population suppressant.” It comes as powder in a bag or can, that you scoop out in teaspoonfuls to place in small piles all around the lawn.
As grub movement and death spreads the bacterium, it increases lawn coverage over several years, lasting up to 20 years in the soil. Ideal soil temperatures for spore development are between 60° and 70° Fahrenheit (19° and 21° Celsius) and keep in mind that it won’t spread unless grubs are present in the soil.
Research indicates that Milky Spore has no impact on beneficial soil organisms. Beneficial nematodes are another alternative control for Japanese Beetle grubs.