Say Goodbye to Grubs

Japanese and European Chafer Beetle Control

Insect-related lawn problems can be frustrating, but the most troubling are insects that dodge the homeowner's radar and feast on grass roots. Because they reside below the surface, root-feeding insects are difficult to detect, and once signs of invasion are evident, the damage is already done. Two species, Japanese beetles (Popillia japonica) and European Chafer beetles (Rhizotrogus majalis) are the most challenging for homeowners in the midwestern and northeastern U.S.This article explains the life cycles of these species and how to control them.

Unwanted Imports

Both Japanese beetles and European Chafer beetles have origins outside the U.S. and were inadvertently imported into this country. Japanese beetles arrived in New Jersey in 1916 and European Chafer beetles came to New York in 1940. Since their arrival, Japanese beetles have spread as far south as the Carolinas and are established in many states east of the Mississippi River, and the European Chafer beetles have been sighted in all northeastern states as far west as Michigan.

The Japanese beetle is a metallic green colored insect with dark green legs. It is oval-shaped and almost one-half inch long. The European Chafer beetle is a little longer and reddish brown in color. Japanese and European Chafer beetles in the grub stage are white-bodied with brown heads, positioned in a c-shape in the soil. Newly-hatched grubs will be less than 1/4 inch long and fully mature grubs can measure up to one inch long. The differences between these grubs are so small that they must be detected with a microscope.

Although these beetles were not considered pests in their native countries due to an ample number of predators, there are no predators in the U.S. that make them part of the food chain. As a result, they can invade lawns very quickly.

Appetite for Destruction

Although both of these species feed on the roots of cool season grasses, their behaviors differ. For instance, adult Japanese beetles are notorious foliage feeders, subjecting many trees and shrubs to defoliation. On the other hand, European Chafer beetles do not generally attack foliage as adults. Another major difference is where the species will lay eggs. Japanese beetles prefer to lay eggs in moist soil, while European Chafer beetles hunt for dry soils, particularly sandy ones.

It's important to understand that the most destructive time for both of these beetles is during their larval stage, otherwise known as grubs or white grubs. A grub-infested lawn will have thinning, wilting grass that looks as though it is drought stressed. Because the roots are no longer present, there is nothing to anchor the grass to the soil, allowing the grass to be pulled up quite easily. Pull the grass back like a carpet and you will likely see small, white c-shaped grubs at the surface, and there are probably many more below the surface.Numbers greater than 10-15 per square foot warrant action, particularly if your lawn is not regularly watered. (A lack of water compromises plant root regeneration after grub damage.

Learning Their Life Cycles

Understanding the beetles' life cycles is essential for successful control.Both beetles follow fairly similar one-year annual life cycles. The eggs hatch in August and then the small grubs feed in the fall, growing quite rapidly. They reside over the winter in the soil and then resurface in April and May to feed again, now as very large grubs. Then, they transform to pupa (cocoons), becoming adults in June and July. (The warmer the soil, the earlier the transformation.) The species fly away to mate, lay eggs in the soil in late July, and then the process starts over again.

Control Measures

Controlling Japanese beetles and European Chafer beetles depends on a combination of timing, soil conditions and the right pesticide.Here are some tips for timing control:

• The best time to control grubs is when they are actively feeding on roots in the fall or spring. The earlier in their life cycle, the better — the larger they grow, the more difficult they are to control.
• Soil moisture plays an important role during the egg laying process. If you suspect Japanese beetles and you water your lawn often, try turning off the water and drying the soil during the time for egg laying (late July). Try the converse for the European Chafer beetles — they prefer dry soil, so watering the affected areas can help detract them.
• The best currently known method for control is to apply a selective insecticide prior to egg hatch, known as Merit^®, Grub-Ex^® (both are imidacloprid) or Mach 2^® (halofenozide). You must apply these insecticides in early July, prior to egg hatch. These products have a residual and will effectively kill the young grubs as they hatch in August. All areas that may have been infected in previous years should also be treated.
• If you miss the July window and suspect grub activity, the best time for control is early fall when the grubs are small. Use Dylox^® (trichlorfon) or Sevin^® (carbaryl) to reduce damage. These products must be combined with water to be effective.

Now that you know how Japanese and European Chafer beetles behave, you can make sure they don't invite themselves to dinner underneath your lawn. Use your knowledge of their life cycles to control them at the proper times, and soon you can enjoy a healthy, grub-free lawn.