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The Japanese beetles have left their mark on Central Illinois with defoliated trees and decimated flowers. Japanese beetles have been and remain one of the most devastating pests for home gardeners and fruit and vegetable growers.

They have many areas to lay their eggs (lawns), lots of food sources and few natural enemies. The milder winters, like the past one, cause their populations to build. For the past six weeks, the adults feed and have caused heartache for many. However, there are some steps that gardeners can take to increase the health of the garden and prepare for the next growing season.

Roses, grapes, apples, crabapple, linden, milkweeds and some of our annual flowers are particularly delectable for these hungry pests. It may be time to reassess the landscape and replace heavy-hit plants with ones Japanese beetles are less likely to attack. Replace your crabapple with a magnolia or dogwood. Replace roses, Rose of Sharon or hollyhocks with hydrangeas. Annuals like moss rose, begonia, impatiens, geraniums and marigolds seem to be resistant to the beetle dominance.

Color can play a role in your plant being attractive. Yellow and white flowers tend to be more heavily damaged than red, pink, mauve or orange.

Start the next season with a plan. Row covers are commonly sold. Cover plants like your beloved Japanese maple at least for the first two to three weeks of Japanese beetle season.

Do not use Japanese beetle traps. Despite these traps being available, they simply do not work to reduce the population in your garden. They only attract more beetles. Unless you live on several acres, you are not saving yourself any headaches.

Trees and shrubs that have been defoliated would greatly benefit from a late-season fertilizer treatment. They have lost some of their energy reserves. We recommend using nitrogen-only fertilizer unless a soil test reveals low phosphorous and potassium levels, which are not common in central Illinois. The numbers on the package will be something like 21-0-0, 33-0-0 or 48-0-0.

Starting one to three feet from the trunk (depending on trunk size), drill holes 12 inches deep around the trunk. Space holes about two feet apart. Keep adding circles until you reach the drip line. Divide the mixed fertilizer evenly between the holes.

Save basil seed to replant a second time in the growing season. As soon as the Japanese beetles started enjoying my basil more than I did, I ripped out the stand and planted a fresh crop.

In addition to knocking beetles in a vat of soapy water, remove damaged leaves during the outbreak. The odor left behind causes the beetles to aggregate on one plant.

Kelly Allsup is the University of Illinois Extension horticulture educator in Livingston, McLean and Woodford counties.


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