How to control Japanese beetles

July 16, 2012

Information from the Morton Arboretum:

- Adult Japanese beetles begin emerging in late June and will continue for six to eight weeks. This insect spends most of the year in the soil as a grub (young form) feeding on turfgrass roots. Growth is completed during June and adult emergence occurs in early to mid-July in northern Illinois. They were 2 weeks earlier this year because of the early spring.

- The adult beetles feed on nearly 300 different plant species and nearly 140 plant families.

- Highly preferred hosts include roses and related species, grapes, raspberries, lindens, crabapples and certain elms.

- The beetles feed on the foliage resulting in a skeletonized appearance. Highly preferred plants may be severely defoliated.

- The adults are about 1/2 inches long, shiny, and have a metallic green or greenish-bronze appearance with copper wing covers. They have five white pairs of spots (tufts of hairs) on both sides of the abdomen.

- If you have a small infestation, a bucket soapy water works. Take the bucket, a few drops of soap and then tap the branch and they drop into the bucket. When you tap a branch, it is a nature response to drop and not fly.

- If you use insecticidal sprays, only spray the plants that are important to you and newly planted trees and shrubs. You don't want to spray the whole yard. More established plants that are healthy and vigorous should be able to tolerate some defoliation.

- They won't kill a plant, they come late in the season so the leaves have done most of their food production, it just looks worse than it is.

- People who are watering their lawn are more likely to get the beetles because the females can lay their eggs easier in a moist well watered lawn vs a dry hard compact soil.

- Stay away from the Japanese Beetle traps. They attract more beetles then the trap can handle and so you end up with a bigger problem.

Help for drought stressed plants/trees:

- The Arboretum recommends watering within the drip line of a tree, from the trunk out to the end of the branches, to reach the roots most effectively. The objective is to keep roots moist but not wet. Avoid frequent light watering. Let a hose run slowly at the drip line of the tree, moving it around occasionally. If using a sprinkler system, place a container nearby and let it fill 1-2 inches.

- "Gator Bags"-plastic, water-filled vessels that envelope a tree trunk-provide a slow drip to the root system and are a good way to keep your younger tree well watered.

- Remember to keep two to four inches layer of organic mulch around a tree to moderate soil temperature and retain moisture. Do not let it touch the trunk or stems.


- Bucket with soapy water

- Hose to show watering within the drip line of the tree

- Gator Bag set up on a tree

- Organic mulch around the base of a tree

Morton Arboretum
4100 Illinois Route 53 in Lisle
Just west of Interstate 355 and north of I-88 on Illinois Route 53 (sometimes known as Lincoln Avenue or Lincoln Highway).
Westbound I-88: Exit north onto Route 53. Proceed north ½ mile to entrance

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