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JAPANESE BEETLES

--- Anne K Moore July 31, 2009 ---
Photos by Anne K Moore ---

Not many things on this planet raise the ire of gardeners more than Japanese Beetles.  Their larvae feed on our grass and flower roots.  Their adult forms feed on our roses and other savory flowers. 

They have some redeeming qualities.  The larvae make good bird food.  If you can look past the ravaged flowers and leaves, you see that these adult scarab beetles are dressed in beautiful metallic copper and sea green.  Well, maybe these are not such redeeming qualities.

Your lawn might also be dug up by skunks and raccoons who like to dine on the fat, dirty-white grubs, larvae of the Japanese beetle, that live underground and chew on roots.  Moles, in particular, tunnel through infested lawns looking for these dinners.  (Did you know?  Moles don't eat roots; they eat the grubs that eat the roots.)  Moles could be considered beneficial if they didn't raise up roots so that the roots dry out in the mole tunnels.

Since we cannot rely on moles, skunks, or raccoons to control the Japanese beetle population, what controls are out there?  One natural control has to do with the weather.  Female Japanese Beetles prefer sunny, soft, warm, moist turf in which to lay their eggs.  If there is a drought during the infestation, next year's beetle population will be light just because the beetles will have difficulty digging and depositing their eggs.  If the drought occurs after the egg laying, then many of the larvae will die.  On the down side, if there are rain showers throughout July and August, when the beetles are actively mating and burying eggs, then there will be a glut of beetles the following summer. 

Hand picking the beetles is a satisfying control.  Track them throughout your garden early in the morning while they are still sluggish.  Hold a container of soapy water under them.  Take advantage of their predisposition to drop when disturbed by just giving a light jiggle to the plant.  Those of you with strong fingers and stomachs can just squish them but I prefer the drop and drown method myself. 

According to the University of Maryland, ''Kentucky bluegrass, perennial ryegrass and fine fescues are the most sensitive to grub feeding damage. Whereas, tall fescue and warm season species such as zoysiagrass and bermudagrass can tolerate moderate to heavy populations during the hot dry conditions that often kill Kentucky bluegrass.''

If you plan to use a biological control then you need to know that you have a large enough infestation for it to work.  According to the U.S. Department of Agriculture, you should use a shovel to ''dig a square hole 8 by 8 by 3 inches deep in the turf. Turn the sod over on some newspaper and search the grass roots and the soil in the hole for grubs. Turn the turf back into the hole and add water to help the grass recover. Record the number of grubs found in the sample location so you can map out or average grub densities. To convert these numbers to the number of grubs per square foot, multiply them by 2.25. Generally, you should consider treating areas in your lawn with more than 10 grubs per square foot.''

The bacterial Milky Disease (Bacillus popilliae Dutky) method takes 2-4 years to build up in the soil and in the grubs so that they re-infest new larvae every year.  Each dead grub releases 12 billion spores back into the soil.  These spores stay in the soil for 20-30 years, even when there are no more Japanese beetle grubs to infest.  What a lovely thought.  And, it is non-toxic to all other insects and wildlife, as well as safe for pets and people.

Another safe biological control is achieved with insect parasitic nematodes (Entomopathogenic Nematodes), microscopic wire worms that search out and kill beetle grubs.  According to Ohio State University, ''Products that contain strains of Steinernema carpocapsae (Biosafe, Biovector, Exhibit, Scanmask) have been marginally effective against white grubs in turf. Preparations containing Heterorhabditis spp. seem to be more effective. Apply the nematodes when the white grubs are small. Irrigate before and after applying the nematodes.''

The University of Maryland has this advice:  ''We do not recommend the granular formulations (of Milky Spore Disease) as they have not been proven effective to date. The spore dust product, "Doom" is recommended for newly established turf. The entomophathogenic nematode, Heterorhabditis bacteriophora, has shown good activity against white grubs and is commercially available as Cruiser. A new product, which mimics the insect molting hormone, ecdysone, and causes premature molting, is Mach 2 (halofenozide). This product has shown consistent and excellent control for a number of white grub species.''  These products might not work as well in other areas of the country.  Check with your local University Extension Service office for recommendations.

Chemical insecticides may work quicker, but they are non-specific and will kill earthworms and beneficials living in the soil.  They must be reapplied every year.  You must also strictly follow all label directions.  Humans, pets, wildlife, including birds eating poisoned insects, can all be harmed if they are exposed to some of these pesticides. There is concern, in addition, that runoff will pollute streams and/or drinking water aquifers. 

According to the USDA, ''While they take a little longer to produce the same results as insecticides, biological control agents last longer in the environment.  More importantly, they do not adversely affect nontarget or potentially beneficial organisms.''

The best time to use biological controls against the Japanese beetle grub is when they are small and near the surface.  The eggs will be hatching soon; the larvae will be starting their feeding and descent to lower ground for the winter.  The best time to treat the soil for next year's Japanese beetle infestation is August, September, October depending on where you live.  Check with your local Extension Service office.  You can order the biological controls through mail order or on-line.  Be kind to yourself and your garden.  Start treatment this fall for a coming year that could be less irksome.

Ohio State University Extension Fact Sheet
USDA Aphis Publication  Managing the Japanese Beetle: A Homeowner's Handbook
University of Maryland Japanese Beetle
GardenSMART - Roses, Show 37
Clemson University Extension Service


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