The Dreaded Japanese Beetle

It is that time of year when the dreaded Japanese Beetle (Popillia japonica) ascends upon us. I had my first sighting of some today. I say "ascends" because they live as larva in the soil and after they pupate, they emerge as adults.

They play havoc with a number of plants, eating the flesh of the leaves while ignoring the veins. In the vegetable garden, they will concentrate on any bean species and they also like blackberries, though they will not harm the fruit. I have noticed that they like to eat taller leaves rather than those closer to the ground when given a choice. For example, if pole beans are available, they will virtually ignore the bush beans. In my yard, I have noticed that they also have certain preferences. Roses seem to be their favorite including the invasive Multiflora Rose. They also gravitate to my Japanese White Birch and Japanese Maple. They loved the Chinese Elm prior to its demise in the aforementioned ice storm. They don't seem to like any of the native oaks or maples. They go completely crazy over the wild grapes as well.

We first observed them here around 5 years ago. They seemed to grow in numbers the first 4 years. I placed traps out in two locations within our 3 acre smallholding. The traps use a pheromone to attract the beetles. When they land on the piece holding the bait, they drop into the bag. The traps must be carefully located. If they are too far from their favorite plants, they will not be drawn to the traps. If they are too close, the traps will draw them to the plants as well. During their peak activity, I would regularly empty a full bag every day at each location.


Our land is surrounded by woods and I began to wonder if I was not simply doing more harm than good with the traps. Was I drawing more beetles from the woods? So last year I did not put up any traps. Not only did I not see as many beetles on their favorite plants, I did not have to empty those nasty bags every day! I have since discovered that a University of Kentucky study indicates that the traps do draw more than protect.

They can be controlled in the larval stage with application of the bacterium milky spore. However, it can take several years of applications to eradicate them. Further, to do so on 3 acres would be too expensive and finally, they can simply fly in from any neighboring area.

I have also noted that the moles have been quite active this year. This is usually an indicator of an increase in grubs. I hope that the grubs that they were feasting on are not Japanese Beetle larvae! I will keep you posted as the season progresses.

Here is a distribution map in case you are wondering if they are heading your way.