Unfortunately, there is no
quick and easy way to control Japanese beetles.
- Many birds eat Japanese beetles and moles, shrews and
skunks feed on the grubs in the soil. Unfortunately, these generally do
not significantly reduce populations of beetles.
Milky Spore Disease - This naturally occurring bacterial disease
kills the grubs of Japanese beetles in the ground. Unfortunately, there
have been no controlled studies that indicated that Milky Spore disease
works in northern weather. In Southern states where it has been most effective,
it gives erratic results.
Hand Picking - If you have only a few plants to protect and low
numbers of beetles, hand picking may work.
Japanese Beetle Traps - Bag traps are generally not effective
especially if they are placed near the desirable plants. Studies have shown
that they actually attract more beetles to the area than would have otherwise
been the case. If using a trap, place it 50 feet or so up wind of the desirable
plants to draw beetles away. Do not place them directly in the flower bed
- Although the beetles spend most of their time
in the soil as larvae (white grubs), treating this stage is often not effective
either. The beetles are strong flyers and may travel a mile or more to
feed so treating the soil on your property only may not help. If you dig
around this fall and find large numbers of grubs ( 5 or more per square
foot), it would warrant a soil treatment with a
product labeled for grubs of Japanese beetle.
Chemical Sprays - The most common approach includes spraying
the adult beetles as they accumulate on desirable plants. This may have
to be done several times during the infestation period. Spray only small
or valuable specimens that need protection to minimize pesticide use.
Products labeled for
Japanese beetle control are often used. An application should provide decent
control for 4 to 7 days. Also, do not expect the beetles to die immediately
upon being sprayed. It often takes a little time for
insecticides to work.
Remember these are generally considered broad-spectrum insecticides
which will kill non-target species such as beneficial insects. So, use
them only as needed and only on plants being seriously attacked.