Adult Japanese beetles seldom become a problem when gardeners are following a regular spray schedule for the control of other insects. But if you find yourself battling the beetles, persistence and the right insecticides are the key to controlling the rose-munching pests.
You can protect the foliage and fruit of most plants by spraying them with insecticides like sevin or malathion. Unfortunately, insecticides will not fully protect roses as they unfold too fast and are especially attractive to beetles.
When beetles are abundant on roses, clip the buds off and spray the bushes to protect the leaves. When the beetles become scarce, let the bushes bloom again. Limited numbers of rose blooms for show purposes can be protected from beetle damage by tying perforated plastic bags or netting over the buds before the beetles appear.
When it comes to tackling Japanese beetles, timeliness and thoroughness are very important. Begin treatment as soon as soon as the beetles appear, before they can do any damage. Use insecticides only on plants for which they are designed, and follow all of the directions on the insecticide’s label. Apply insecticides thoroughly, so that all parts of the plant are covered. More than one application may be necessary to maintain protection, especially of new foliage and ripening fruit. Most Japanese beetle insecticides will control the insects for about a week, but additional applications may be necessary after heavy rains.
When insecticides are applied to edible plants, it is important to observe the required waiting period between the last application and harvest. This is specified on the insecticide container label. To be doubly safe, always wash edible plant parts before cooking or eating them.
Japanese beetle traps impress a lot of home gardeners, but they may not always be effective.
These traps work by attracting beetles and can actually increase the number of beetles you are fighting against.
However, they can work well if you are trying to draw the beetles out of a small area like a rose or vegetable garden. In that case, place the traps on the outer edges of you garden to lure the beetles away from your prize plants.
(Frank Watson is the University of Georgia Extension agent in Wilkes County, Ga.)