Japanese Beetles bring big appetites for plants to Ozarks
SPRINGFIELD, Mo. — Adult Japanese Beetles are on the rise again in the Ozarks, although some gardeners have yet to see one while others seem to be afflicted in abundance.
Those who have them know they bring a voracious appetite, says Patrick Byers, horticulture specialist, University of Missouri Extension. Why they declined in population the past couple of years depends on you ask, from cold winters to drought conditions that can vary widely.
“These insects can quickly defoliate over 300 different types of ornamental landscape plants by eating the tissue between the veins of leaves and flowers, a type of feeding called skeletonizing,” Byers explains.
Trees and shrubs most attractive to adults include: Japanese and Norway maple, birch and pin oak, sycamore, plums, elm and cherry trees, rose, willows, lindens and Virginia creeper. The grubs will also feed on a wide variety of plant roots of ornamentals and turfgrasses.
“Roses, crepe myrtle, grapes and the Japanese maple seem to be the beetle’s favorite food. The main concern in our area is adult beetle damage to broad-leaved plants,” says Patrick Byers, Springfield-based horticulturist for the University of Missouri Extension Service.
Adult Japanese Beetles are a brilliant, metallic green color, generally oval, 3/8 inch long and one-quarter of an inch wide. The wing covers are copper-brown and the abdomen has a row of five tufts of white hairs on each side. These white tufts are essential to the insect identity.
There are four main control strategies available to the homeowners:
Hand picking. “When the first adults arrive on a property, you can pick off these scouts (which attract more pests) and destroy them by dropping them into soapy water,” says Byers.
Knock them off leaves into a bucket with two to three inches of soapy water. Early in the morning or just before sundown are when the beetles are most sluggish and easiest to capture.
“The natural defense of Japanese beetles is to drop straight down when they feel threatened. If you put the bucket with soapy water under the leaves you can usually slide them into the bucket,” says Byers.
Use traps. “Traps have been demonstrated to be effective in reducing damage and populations only when several neighbors use them together or when you place one trap far away from a plant you are trying to save,” says Byers.
Otherwise, traps attract more beetles into the area than would normally be present and more beetles than are actually caught.
“If you use traps, place them at least 50 feet away from the plants you want to protect,” said Byers.
Insecticide Spraying. “Foliage can be protected with sprays of pyrethrins, rotenone, methoxychlor, malathion, and carbaryl (Sevin). Repeat applications (every 10 days) are often necessary for management of this pest,” said Byers.
Neem oil has also been found to drive off Japanese beetles.
Direct spray applications of insecticidal soap kills Japanese beetles on contact but does not provide any residual protection.
Natural Protection. “Milky Spore is a natural bacteria that attacks the Japanese beetle in the grub stage. Spores in treated turf are swallowed by grubs during normal feeding,” said Byers.
Milky Spore disease kills the grub in one to three weeks of infection. As the grub decomposes, it releases billions of new spores into the soil to infect more grubs. Milky Spore is not harmful to beneficial insects, birds, bees, fish, pets or man and will not affect wells, ponds or streams.
The downside is that spore count must build up for two to three years to be effective. During this time you should not use an insecticide against the grubs since they are needed to complete the bacterium cycle.