Japanese beetles aren’t just a scourge on ornamental gardens but feed on hundreds of different plant species making them well adapted to a variety of landscape types.
Being this well adapted makes them very difficult to control. Adult Japanese beetles aggregate, feed and mate in large groups after they emerge, causing great damage. They feed on the upper leaf surfaces, skeletonizing the tissue between the primary leaf veins. If the populations are high, they can remove all of the green leaf material from an entire plant. With the leaves flesh stripped away, they are left with nothing but their veins and midrib making them useless to the tree. Japanese beetles may feed on other plant parts including burrs, cones and developing flowers.
These beetles are strangely beautiful. They are roughly 3/8″ long and 1/4″ wide. They have shiny, metallic-green bodies and copper-colored wing covers. Adults emerge, feed and mate throughout the summer and lay their eggs in the soil from summer to early fall. Larvae hatch about ten days later and begin feeding on grass roots. As the temperature cools in the fall, the larvae go deeper into the soil to avoid the frost. In the spring, they move back up and emerge as adults in early summer once again.
Containing an infestation when it is small is ideal but often times a population goes unnoticed until it is already out of control. The best time to treat for Japanese beetles is late July through mid August.