--- Anne K Moore
July 31, 2009 ---
Photos by Anne K Moore ---
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.
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
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 1–2 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
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
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
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