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INDIANAPOLIS – Japanese beetles have been reported across areas of central Indiana, an invasive species of beetles that can cause damage to plants. Ren Hall, a Nursery Inspector and Compliance Officer with the Indiana Department of Natural Resources Division of Entomology and Plant Pathology (DNR DEPP), explained what they look like, and how to treat the issue depending on the severity of the problem in your garden, and how to report seeing them.
Japanese beetles are native to Japan and were accidentally introduced into the U.S. over a hundred years ago. Since then, they have spread across most of the U.S. Most states are considered infested or partially infested with these beetles, while others are considered non-infested or have quarantines in place to try and prevent the spread.
Adult beetles lay eggs in the summer, usually in July and August. When the eggs hatch, the larvae burrow into the soil and remain there, feeding and growing until the following year. In spring, the larvae turn into pupae. The pupae turn into adults starting in June. In Indiana, we see adult Japanese beetles usually in late June to late August and sometimes into September.
The adult Japanese beetle has a shiny green head and thorax, copper brown wing coverings, and is roughly half an inch long.
Japanese beetles feed on over 400 known host plants with their favorite ones including lindens, roses, raspberries, Japanese maples, apple trees, grape vines, hydrangea, and other common nursery plants.
In different stages of their life, they live underground for a time and can eat the roots of plants including turf grass on which they are considered a significant pest.
The larvae, which live underground, cause damage to the roots of plants which then have a hard time taking up water and nutrients from the soil and can lead to dead brown patches of grass. Adult Japanese beetles damage plant leaves, eating the green tissue between the veins. When feeding damage is heavy, leaves are skeletonized and all that is left are the veins.
Depending on the severity of the problem will depend on how to treat the issue. If it is a small infestation, knocking the beetles into a bucket of soapy water works fine. Inspect your plants frequently during the active period, mainly in the summer months.
For any larger area where hand-picking is not feasible, Hall recommends an integrated pest management strategy for any pest, not just Japanese beetles. Integrated pest management (IPM) is a system where no single pest management strategy is used exclusively, instead, a combination of methods is used (such as chemical control, biological control, cultural control, etc.). In other words, there is no “one size fits all” treatment for most pests. IPM is important to help avoid pesticide resistance which can develop in pests when chemical treatments are overused, used incorrectly, or used as the only control method. Knowledge of the pest’s life cycle should also be taken into account so that early detection can occur and treatments can be timed to coincide with the life stages they target.
Insecticides are available for the control of adult beetles, but repeated treatments are likely to be needed. Make sure the product you use is labeled for Japanese beetles. If Japanese beetle feeding damage bothers you but you don’t want to use an insecticide, first and foremost try to avoid planting their favorite plants. Plants that are damaged by Japanese beetles may exude a chemical known as a kairomone which unfortunately may attract more beetles, so it’s best to control the problem when the infestation is small, rather than waiting for large numbers to be present. It is not recommended to use Japanese beetle traps because they may attract more beetles to the area than they actually catch, leaving the ones they didn’t catch to feed on your plants.
For turfgrass, regular watering of grass during spring and summer is one cultural method of preventing damage by grubs (although irrigation during adult active periods in summer may increase desirability for laying eggs in that area). Both curative and preventive insecticides are available for larvae in turfgrass.
If you live in Indiana, there is no need to report Japanese beetles as Indiana is considered generally infested, meaning the beetles are already widespread.
If you are interested in learning more about plant pests and pathogens and invasive species in Indiana, please subscribe to their newsletter, the Entomology Weekly Review. Here is the link: https://secure.in.gov/dnr/entomology/entomology-weekly-review/. You can also contact the DNR DEPP at DEPP@dnr.IN.gov or 317-232-4120.