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Japanese Beetles Are Now Swarming

Timothy J. Gibb and Cliff Sadof, Extension Entomologists

Japanese beetles are beginning to aggressively defoliate trees and flowers in many parts of Indiana. They feed on most flower blooms and a wide range of deciduous trees and shrubs especially linden, sassafras, sycamore, Norway maple, birch, elm and flowering fruit trees. Newly transplanted trees or plants that are stressed are particularly susceptible to damage. Japanese beetles are usually a pest for about 6 weeks, however, with earlier than normal emergence of the beetles this year; they may be around for up to 8 weeks. After feeding on leaves and flowers the beetles mate and lay eggs in turfgrass where they become the white grubs that damage home lawns. Many people ask whether killing one will prevent damage by the other. What we have found is that killing beetles as they emerge from the turfgrass will not prevent plant defoliation because adult beetles fly long distances to find suitable plants to feed on. In reality, very few of the beetles feeding on your trees and flowers actually originated from your turfgrass. The same is true for control of Japanese beetle grubs in turfgrass. Controlling the adult beetles on trees and shrubs will do little to prevent grub damage. Therefore, from a control perspective, adult defoliation and grub damage should be treated as two separate problems.

Controlling defoliation: if Japanese beetles are causing heavy injury in your area by July 1 you will probably need to apply some insecticides. Unfortunately, repellents do not provide effective controls. Beetles are far more attracted to floral scents and the smell of freshly chewed leaves than they are deterred by applications of repellants. Soil applied insecticides are only marginally effective in high populations, because adults must consume the poison-laden leaves to be killed. Foliar sprays of pesticides can provide control. To get the best control, spray 2 or 3 times at regular intervals. Carbaryl (sevin) is commonly used by homeowners and provides about 7 days of control. Some new materials, called pyrethroids, have just hit the home market. These materials provide control for over 2 weeks. There are several of these materials on the market for homeowners sold under a wide variety of trade names. Look for one of the following the active ingredients: permethrin, esfenvalerate, cyfluthrin, or bifenthrin. All of these products are toxic to fish; so extreme care should be used when applying these near bodies of water. In addition, they all are toxic to honey bees, so care should be taken about spraying flower gardens that are being visited by bees.

Controlling grub damage: the fact that the adult beetles are out earlier this year, also means that the eggs will be laid in turfgrass and will hatch into White grubs sooner as well. Insecticides available to the public for grub control the active ingredients; bendiocarb, diazinon, trichlorfon, isofenphos, or carbaryl (sevin). Any of these materials can be used as rescue treatments. This simply means that the chemicals work if applied after the grubs have hatched - usually the end of July or the first part of august, depending on where in the state you live. Two other very effective grub control products must be used differently. These include imidacloprid (Merit) and halofenozide (GrubX, Mach 2). Both products are very long-lasting but must be applied as preventative treatments - in late June or during July. As with all homeowner-applied insecticides, it is critical to follow the label directions exactly when making applications. For grub control products it is recommended that granular formulations be used and that 1/2 inch of irrigation be applied immediately after treatment. In cases where irrigation is not possible, timing the application to just before a significant rainfall event is recommended.

You may also view this information as a PDF (98K) document at: http://www.entm.purdue.edu/Entomology/ext/targets/HN/HN-21/HN-21.pdf

The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by the Purdue University Cooperative Extension Service is implied. Any person using products listed assumes full responsibility for their use in accordance with current direction of the manufacturer. Purdue University is an equal opportunity/equal access institution.

Information listed is valid only for the state of Indiana.

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