The Purdue Plant and Pest Diagnostic Laboratory

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June 8, 2007

Early Japanese Beetles

Tim Gibb, Insect Diagnostician, Department of Entomology, Purdue University

Doug Richmond, Department of Entomology, Purdue University

It seems that the Japanese beetles have been arriving early for the last few years but this year is truly an exception.  The first Japanese beetles of the year were observed in central Indiana on the 3rd of June.  This is a full week earlier than we have EVER seen them here before.  Normally, Japanese beetles arrive in this area about June 20th or so.  We expect them reach full force within the next 2-3 weeks and begin feeding on their favorite plants.  Plants particularly at risk include those that have been recently transplanted or those that are stressed for one reason or another. Favorites for Japanese beetle include linden, crab apple, plum, and other fruit trees, rose bushes, grapes, and several garden variety vegetables.  Physical (netting or picking off the beetles each day) or chemical controls (Sevin, Neem, Orthene, Malathion or any of several pyrethroids) may be required to protect plants from Japanese beetle defoliation.  Defoliation usually begins at the top of the tree and works its way down.  Leaves become skeletonized such that only the midrib and major leaf veins are left (see photo).

After adult beetles feed, and mate, the female often lays her eggs in turfgrass areas.  The resulting larvae, called white grubs, can also be very devastating as they prune the roots off of the grass. Insecticides available for grub control only work AFTER the grubs have hatched - usually the end of July or the first part of August. Effective grub control products include imidacloprid (Merit) halofenozide (Mach 2) thiamethoxam (Meridian), clothianidin (Arena) and we expect yet another very effective compound to be released in the near future.  These products are long-lasting but are most effective if applied from late June through July.  As with all insecticides, it is critical to follow the label directions exactly when making applications.  For grub control products it is recommended 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.

Early Japanese Beetles - HN-45-W (pdf file)

Click image to enlarge

Japanese beetle

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service