Japanese Beetles

I went down to the Kaleidoscoops (I am a shameless promotor of our local stores and besides my daughter Alexa works there) for ice cream after dinner and as I was eating I was struck by the damage done to the trees by the Japanese beetles. You have probably seen this on trees around town. The tops of the tree canopy are brown from the beetles eating the leaves. The liquid amber tree in my neighbor’s yard is similarly affected. Obviously, this defoliation is not good for the tree, but it will not kill it. In fact, if you look closely you can probably see new growth already starting.

A friend of mine with whom I worked a few years ago told me that he had noticed that the Japanese beetle population had increased as our winters here became milder. I asked him if he thought a few severe winters would decrease the population and he didn’t think so. So what can we do?

It helps to understand the life cycle of the beetle to know what type of control to use and when to use it. Right now the beetles are eating and mating and laying eggs in the soil. These eggs will hatch into grubs. As young grubs they will be in the top couple inches of soil, but as we move closer to winter and they mature they will move deeper in the soil. They move back up to the soil surface in the spring when the soil warms and feed some more. The next stage of their life is as a pupea. Similar to how caterpillars spin a cocoon to turn from caterpillar to butterfly, the grub pupates and then emerges as the adult beetle in late June to early July.

For this year, there isn’t much we can do. Use Eight® (permethrin) or Sevin® (carbaryl) as a spray to kill on contact. Please be careful to spray when there are no bees around. Lori always recommends using the beetle traps, but they can attract beetles from as much as 5 miles away and they only trap about 75% of the beetles, but at least you know the ones you did trap will be dead.

Starting now you can put down a grub control on the lawn and in the garden beds. Use a grub control that contains imidicloprid. Another product is Milky Spore®. This is a biological control that colonizes in the soil and also kills the grubs. As young grubs they are more susceptible to the grubicides and biological controls.

To protect your trees and shrubs next year, use a systemic insecticide. These are applied either as a drench (poured at the base of the tree or shrub) or a spray. There are several on the market that are effective for an entire year. So either now or next spring apply the insecticide (imidicloprid). It takes about 4-6 weeks for the insecticide to move up the tree to be effective so do it before the end of April.

Another thing to do is to choose plants that they don’t like. These include: ageratum, arborvitae, ash, baby's breath, garden balsam, begonia, bleeding heart, boxwood, buttercups, caladium, carnations, Chinese lantern plant, cockscomb, columbine, coralbells, coralberry, coreopsis, cornflower, daisies, dogwood (flowering), dusty-miller, euonymus, false cypresses, firs, forget-me-not, forsythia, foxglove, hemlock, hollies, hydrangeas, junipers, kale (ornamental), lilacs, lilies, magnolias, maple (red or silver only), mulberry, nasturtium, oaks (red and white only), pines, poppies, snapdragon, snowberry, speedwell, sweet pea, sweet-William, tuliptree, violets and pansy, or yews (taxus).