japanese beetles

Japanese beetles have invaded gardens in Illinois in their annual feeding frenzy. The arrival of the pests each year signal concern among farmers and gardeners.

It’s time again for those shiny, greenish-copper little bugs to start showing up in large numbers. You see them at night on your door screens and sometimes inside the house, thumping against the walls or flying into someone’s hair. But even worse, they are in your gardens and fields. In a brief visit to one backyard garden in Shelbyville, eleven were found on single morning glory leaf and many others were seen grazing on tomato, pepper, cucumber, and squash leaves. Dead tree leaves litter some streets and cars, reminiscent of an early fall.

Japanese Beetles pose a threat each year to Illinois crops and gardens and according to the University of Illinois Extension Office in Champaign; they are hungry and unpredictable eaters. “Japanese beetle adults feed on more than 300 plant varieties, showing a preference for some plants over others, thus damage to preferred plants is more severe.” Those ‘preferred’ plants cover a wide range, including smartweed, crabapple, linden, birch, willow, rose, grape, apple, peach, and brambles. But like the proverbial Tasmanian Devil, there are other plants that are fair game, like corn and soybeans.

The Champaign office added, “In corn, Japanese beetles cause injury both as grubs and adults. As grubs, they feed on root hairs, interfering with the uptake of water and nutrients. Injury caused by grubs will often go unnoticed until plant growth and development is affected.”

Locally, Jim Looft Director of the University of Illinois Extension Office of Shelby County commented, “There is reported damage to ornamental plants, shrubs and trees in the area—those kinds of things. Several varieties of garden plants have also had damage of some sort.”

Looft echoes the comments of other agricultural specialists. “The beetles have been getting into sweet corn and eating the silk which affects corn pollination. When the pollen falls, if they have eaten too much of the silk, you don’t get a high level of pollination. We have pollination going on now and some just aren’t ready to pollinate. The damage can be significant.”

Japanese beetles can also cause problems with soybean reproduction. U of I Integrated Pest Management states, “In soybeans, grubs also feed on the root hairs of seedling plants, though the injury is generally not of economic importance. The main threat of Japanese beetle adults in soybeans is the defoliation of soybean plants. Much of the defoliation of soybeans occurs during the reproductive stages of plant development. Feeding on flowers may interfere with pollination.”

Local gardeners have kept Terry Snoke of Niestradt’s Nursery busy fielding calls. “We have had a lot of calls about them. Several people come in or call every day on the beetles. People are asking what they can do and inquiring about what kinds of insecticides work.” Snoke also said she has noticed the beetles have a sweet tooth for ornamental apple, plum, roses, and Japanese elms. “They seem to like leaves with a red color,” she added.

But it could have been worse, said Looft. “Fortunately, they came early enough this year so it wasn’t as bad as a few years ago when we had many fields with reduced yields.” He also commented on the unpredictability of the insects. “It is hard to determine the economic threshold, when to apply spay. No doubt about it, we’ve been hit. Right now, it’s hard to say what damage we have sustained.”

Michael Gray, entomologist of the U of I Crop Sciences Department stated, “Predicting future infestations of Japanese beetles would most likely be frustrating and often futile. However, one can generally anticipate economic densities of Japanese beetles after mild winters, followed by early planting (the first 2 weeks of April). Infestations also are the greatest in east-central Illinois where there is a history of repeated problems with this insect.”

U of I also states that, “Attacked ornamental plants in obvious locations in the landscape can be sprayed with carbaryl (sold as Sevin), cyfluthrin (sold as Tempo, Bayer Advanced Garden Insect Killer), or other pyrethroid. An application typically controls the beetles for about 2 weeks.” Snoke also said, “We have been spraying with carbaryl, it is sort of like sevin dust in liquid form.”

North of Shelbyville, Rick Pontious of White Heath, IL reported that his blueberries and cherry trees were all but devastated. "They go after everything," said Pontious, who operates a farm about 15 miles southwest of Champaign where customers pick their own produce. "The bushes were just looking fantastic and then all of a sudden the beetles came in," he said. "Last year I thought was bad. This year is worse," he added.

.Looft also said, “When the Japanese beetles come is just hard to predict as where. I have seen them eat the old leaves and leave the young tender ones. It is a cycle we have to endure each year. Some farmers will be affected and some won’t. Nobody knows why they will prefer one field over another or one leaf over another. Which fields they will hit hardest is just a random chance.”

The good news, if any, is that the Japanese beetles have their season, about six weeks, and then they are gone. For those who plan to treat, that would entail three applications of sevin or carbaryl.

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