If you had problems last summer with Japanese beetles on your property, the odds are very good they will be pests again this year. In fact some people are already seeing them in high numbers. So what can you do?
Japanese beetles will not kill a tree unless the tree is extremely stressed and already dying. Healthy trees can tolerate leaf feeding by these insects. If you have edibles or ornamentals like grape or roses, the beetle damage will be more destructive and you may opt to treat these plants. Whether or not you decide to treat, always provide deep watering to affected trees and shrubs during times of drought to help buffer the stress of leaf damage.
- If you find Japanese beetles on a healthy established tree, there is no need to treat it.
- If you find them on a newly planted tree or small shrub and there are few beetles, try hand picking them and dropping them into a bucket of soapy water.
- If you can't tolerate the way your trees or shrubs look, you could use an insecticidal spray, but keep in mind it only remains on the tree for about two weeks and may need to be reapplied. You will also kill beneficial insects and/or pollinators that visit flowers. To protect bees, apply insecticides during the late evening after bees are no longer active. Another treatment option is a systemic insecticide which will make the leaves and other plant parts (except rose petals) toxic to all insects (including pollinators) for a season.
- The grub is the immature stage of the beetle and they can cause large dead spots in your lawn. If you have grub damage in your lawn, you could apply a granular insecticide now through early September to keep Japanese beetles from emerging next summer. Beetles often fly to other areas to look for food sources, so even if you see leaf damage it doesn't mean they are laying eggs and hatching as grubs in your yard.
- Research has indicated the pheromone traps/bags are not effective, since they just attract more beetles to your yard.
- Japanese beetles are only active for six to eight weeks, so leaf feeding typically ends around early August.