August 1, 2001
Stillwater Gazette
Betsy Halden

Japanese beetle invasion

You may be seeing a new pest invader in your garden. The pest is the Japanese beetle. Japanese beetles have become a serious invader pest in our area. They’ve been identified in St. Paul, Hastings, and Stillwater. We don’t want them.

When I was growing up in western Pennsylvania Japanese beetles were endemic. They ate grass, shrubs, trees, and flowers. They ate my dad’s roses. We don’t want them in the St. Croix Valley..

The Japanese beetle is a serious pest of grass and ornamental plants. Grubs feed on the roots of the turfgrass. The larval or grub stage of the Japanese beetle is a “C” shaped white grub that lives in the soil. Its primary food source is grass roots. It is know to also feed on the roots of corn, beans, tomatoes, and strawberries. All “white grub” species are similar looking but vary in life cycles, so identifying the grub to species is important for the proper timing of pesticide application. Japanese beetle grubs can cause significant damage to lawns by chewing off grass roots and reducing the ability of grass to take up enough water to withstand stresses of hot, dry weather. Large dead patches of grass can develop in grub infested areas. The sod on these dead patches can be rolled back like a carpet to expose the grubs and the lack of turf roots. Early recognition of the problem can prevent destruction.

Adult Japanese beetles feed on the foliage of over 300 plant species. The list includes prized and cherished roses. Adult Japanese beetles are similar to Junebugs in general appearance but are only 3/8 inch long and ¼ inch wide. the head and thorax are shiny metallic green, and the wing covers are coppery red to a metallic dark tan.. The distinguishing feature is a row of five white hair tufts on each side of the abdomen and two small patches of short white hairs on its rear. If the beetles does not have these patches, but has the other color traits, then it may be the false Japanese beetle.

It is important to control Japanese beetles They eat and defoliate garden vegetation. One control option is removing beetles by hand. This works when only a few beetles are present on smaller garden plants. Remove the beetles when you first see them. This will help to avoid beetle damage or injury to the plant which will attract more beetles. Beetles are sluggish in the morning and can be shaken from small plants into a bucket of soapy water. Screens and cheesecloth or floating row cover cloth can be place over high value plants, such a roses and fruit.

Several traps specific to Japanese beetles have been developed to capture adults. Unfortunately, recent data from Iowa indicate that these traps do not significantly reduce grub populations. In some cases they may contribute to increased defoliation by the beetles. Traps may attract more beetles than they capture.

Certain insecticides may help to control his pest. Many contact insecticides are labeled for Japanese beetle adult control. Common choices on ornamental plants include Sevin, permethrin, malathion, Orthene, and rotenone. Diazinon can be used, and it binds strongly to the soil. It can be used as a rescue treatment when damage is observed. Choose carefully. The insecticide should match the treatment site, such as flowers, trees, vegetables, fruits. Read the label carefully to determine which plants the product should be used on. You may need to make repeated applications. If it rains soon after you apply the insecticide the residual effect of the product may be short lived. When treating a food crop observe waiting days from the last application to the harvest. Do not spray plants in bloom. Treat plants in the late afternoon after honey bees have left for the day.

If you have, or suspect you have Japanese beetles, publications from the University of Minnesota Extension Service and Minnesota Department of Agriculture can help you identify and control the beetles. You can contact Doree Maser at 651.296.1348 for a colored brochure that identifies the beetles. You can also view a new publication called “Japanese Beetle Management in Minnesota” from the University of Minnesota Extension Service by going to www.extension.umn.edu on the Internet. This document has colored pictures and graphics to help identify the authentic Japanese beetle.

Gardening in dry weather
As I write this our extended hot dry spell has ended. Hopefully we will have a balance between heat and moisture during the remainder of the season. Many gardeners ask how they can preserve their lawns and gardens. Briefly, water, water, water, deadhead, and mulch. Most lawns should be sprinkled so that the soil is wet to a depth of five or six inches. Lawns on hot, south-facing slopes, newly established lawns, or lawns with patch disease need frequent shallow watering. Young trees need special consideration.

Mulch should be about three inches deep in flower and vegetable gardens. This will help to reduce the evaporation of the moisture in the soil, and deter weed growth. Grass clippings, straw, chipped leaves and shredded newspapers work well. Woodchips, shredded bark and cocoa bean hulls will accomplish the same thing, but they are better suited for use around woody plants and perennials.

For more helpful information on coping with hot dry spells visit the Yard and Garden news at www.extension.umn.edu/projects/yardandgarden/YGLNews/YGLNews. Go to “Coping with Dry Weather” in the July 15 issue of Yard & Garden Line News.

Betsy Halden is a Master Gardener with the University of Minnesota Extension Service. University of Minnesota Extension Service materials were consulted in the preparation of this column. You can reach Betsy Halden at eahalden@comcast.net