Japanese Beetles

Japanese Beetles

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• When you talk about Japanese Beetles, you are really discussing the two forms of this pest: the larvae in the soil and the adult beetle on your plants.
• The larvae (also known as grubs) are worms (like caterpillars) that live in the soil and eat grass roots. If you have dead spots in your lawn, this might be due to Japanese Beetle grubs.
• Eggs laid in August hatch into grubs that grow quickly. An August application of insecticide will help control these young grubs. After overwintering, the grubs start to feed again in May, so insecticide can be applied to turf from May until mid-June. After that, these grubs go dormant as they turn into adults.
• Killing the grubs in your own yard won’t really protect you from adult Beetles, as they fly well and will come to your yard from far and wide. It will protect your lawn from grub damage.
• Insecticides recommended to control grubs are:
  1. ‘Grub Killer’ by Bayer. The active ingredient is Trichlorfon.
  2. Other products that contain Imidicloprid as the active ingredient.
• The adult beetle is what you’ll really notice. These Beetles emerge in early July and fly toward vines, Linden trees, Birch trees, Roses, and some Apple trees. They don’t stop there (they eat the leaves of lots of plants), but if you are watching you’ll notice them on these plants first. They start eating on the high parts, so look upward!
• As they eat, the damaged leaves emit an odor that attracts other Japanese Beetles. The Beetles themselves also emit an odor that attracts more of their kind.
• If there aren’t too many beetles, you can knock them off the plants into a pan of soapy water.
• If you have a full invasion, you’ll need to spray the plants thoroughly. Suggested insecticides are ’Eight’ or ’Sevin’. Probably two applications, 10-14 days apart, will be necessary.
• Soil applied products with Imidicloprid (as the active ingredient) will be absorbed by the plant and move into the leaves. These can also do a good job of killing beetles. It takes days for this to get from the roots system into the leaves, so apply this very early in the Japanese Beetle season