Japanese Beetles

Posted 6/9/19

Remember the line from that old Poltergeist movie “They’re Back”! Well, here it is early June and just like clockwork we have been seeing the beginning of the emergence of those dreaded “baby …

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Japanese Beetles


Remember the line from that old Poltergeist movie “They’re Back”! Well, here it is early June and just like clockwork we have been seeing the beginning of the emergence of those dreaded “baby June bugs” that eat all of our plants down. Actually, they are not June bugs at all but rather Japanese beetles.

Japanese beetles are about ½ inch long and are metallic green in color with a very noticeable pair of bronze colored wing covers. They have five tufts of white hairs that project out from under their wing covers on each side as well as a sixth pair of white hairs at the tip of their abdomen. The white tufts of hair appear as small white dots when viewed from above. In all actuality they are fairly attractive insects (attractive as far as bugs go that is) and they actually do resemble miniature June bugs as many people describe them to me. Their attractive appearance; however, is about the only good thing that I can say about them. Japanese beetles are a highly destructive insect in both their larva (grub) stage as well as the adults that are out in tremendous numbers right now. In fact Japanese beetles have been known to feed on more than three hundred different plants. Among their favorites are anything in the rose family, crape myrtles, fruit trees, and Japanese maple just to name a few.

Japanese beetles usually begin to emerge from the soil by late May or early June with late June being the peak time for emergence in our area. This emergence pattern will generally taper off in July but we may have encounters with emerging Japanese beetles all the way through fall of the year. Once they have emerged, the beetles immediately begin to feed on your landscape plants and to make matters worse they release a pheromone scent that attracts other Japanese beetles. 

Did you ever wonder how there got to be so many of them? Each female Japanese beetle can lay between 40 and 60 eggs during her lifetime. Most of the eggs are laid by mid to late August. The eggs hatch in one to two weeks and the larvae then overwinters in the soil as a grub.

Control of Japanese beetles is far from easy, as many of you have discovered. This is a result of their very aggressive feeding habit, which results in the total skeletonized appearance of the damaged foliage, as well as the potential high number of beetles out there. By noticing when the first adults arrive on your favorite shrub or bush, you can hand pick them off and destroy them before they have a chance to cause damage and release the pheromone that will soon lead Japanese beetles to your shrubbery by the hundreds. They can easily be killed by dropping them into a container of soapy water. Fortunately, it seems that Japanese beetle populations (or at least the number of calls I get about them) have been steadily decreasing over the past few years as compared to when we first began to see them 15 or so years ago.

Believe it or not Japanese beetles will not eat everything that grows. Among the plants that Japanese beetles do not particularly care for are begonias, boxwoods, forsythia, hollies, hydrangeas, junipers, and pines. 

They also cause little or no damage to dusty miller, euonymus, magnolia, or caladiums.  They will cause some damage to oak trees but usually will attack other plants first. You can reduce the amount of Japanese beetle damage by replacing some plants in your landscape with plants that do not attract them.

Adult Japanese beetles can also be killed with careful application of chemical insecticides. There are several such products that are labeled for use on most home ornamentals including carbaryl (Sevin and other similar products), cyfluthrin (Bayer Lawn and Garden Insect Control and other products), permethrin (sold in a variety of products), and many others. Products containing imidacloprid and bifenthrin also work against Japanese Beetles. Make sure that the product you select is labeled for use on the plants you will be spraying and be sure to carefully follow the labeled directions on the container. Also take extra precaution about applying and insecticide product to things that are in bloom to help protect our honey bees and other pollinators. You should also target your spray application for either very early in the morning hours or late in the evening when bees tend to be less active.

During heavy adult emergence plants will need to be sprayed every few days. Many homeowners become discourage and think that the insecticide that they selected is not working. Actually it is working in most cases but the Japanese beetles emerge so fast and in such large numbers that they are just overwhelming. As I mentioned earlier their numbers even at peak emergence seems to be dropping, so hopefully multiple spray applications this year will not be needed.

There are also Japanese beetle traps available. Don’t fall into the trap trap. In most home landscapes, using one or two traps may even do more harm than good. Remember the traps use a pheromone to attract Japanese Beetles. While a lot of Japanese beetles will fall into the trap…many will not. The ones that do not will release pheromone and attract even more beetles into your front yard. I once got so frustrated with Japanese beetles that I hid a couple of the traps in my next door neighbors yard in hopes of attracting them from my yard over into his. The traps work good to monitor for beetle emergence but are not that effective as a control method…. And besides, my neighbor is still mad at me because his roses got eaten up.

Treating your lawn for grubs during the late summer or early fall can reduce localized populations of Japanese beetle grubs, and is warranted in cases where grub populations are causing damage or thinning to your turfgrass. It is essential to get good thorough coverage of the lawn area to effectively treat for grubs. Often times you will find it much easier to enlist the services of a lawn maintenance professional who is licensed in turf and ornamental pest control to make the application for you. Treating for grubs will not guarantee you will be Japanese beetle free as the adults are very strong flyers and can move up to two miles during their flights.