If you have never heard of skeletonization before and think that a red squiggly error line should show up underneath it, you are not alone. It was not until I was researching Japanese beetles that I came across this term. And don’t worry, it’s not humans or animals that are being skeletonized, but rather the leaves of plants that fall victim to the invasive Japanese beetles. Skeletonization gets its name because when the beetles are done feeding, only the structural “skeleton” of the leaf remains. The veins of the leaf stay intact, but the beetles eat all of the leaf tissue in between and around each vein.
You could probably guess that Japanese beetles originated in Japan. There, they are not a major pest because the beetle’s natural enemies are there to keep the populations in check. In 1916, the first Japanese beetle was found in the United States. They were first introduced in New Jersey likely in a shipment of plant bulbs, and since then they have spread to most states east of the Mississippi River. There are some sporadic populations in states further west however.
If you have roses in your home garden, you may have had to deal with Japanese beetles before. Roses, crape myrtles, zinnias, and marigolds are all favorite food sources of the Japanese beetles. Each beetle alone does not eat much, but in groups they can be quite devastating to foliage. Skeletonization of a leaf prevents that leaf from photosynthesizing and ultimately kills it. Large enough populations of Japanese beetles can kill the plant with their feeding habits.
If a large population of Japanese beetles establishes in your garden, you can treat the adults with either carbaryl (Sevin), or dinotefuran. If you decide to spray pesticides though, it is recommended that you spray in the evening when non-target insects like pollinators will be less affected.
In the United States, there are a few native and a few introduced enemies that make biological control of Japanese beetles a possibility. The soil-dwelling grubs are major pests of lawns because they feed on grass roots. They can be managed by a few species of nematodes and fungi as well as the more commonly known and used bacteria, Bacillus thuringiensis (Bt).
Traps are a great tool to monitor for the presence of Japanese beetles. The only problem is that sometimes the traps are so good at attracting the beetles that more come than can be caught in the trap. This leads to nearby susceptible plants being even more prone to damage than when traps were not present because more beetles are in the area. To use traps efficiently as a monitoring tool, remove the trap as soon as a few beetles are caught. This way, you already know that there are beetles in your area, but you are not attracting more to your garden.
There is currently no set damage threshold for home gardens, so deciding to treat is a matter of deciding how much the plant(s) mean to you as compared to the effort you would have to put in to manage the beetles. Small populations of Japanese beetles may not need treatment. They will move on in a afew short weeks, and the plant can recover without treatment. An easy and quick way to try to mitigate the problem without any supplies though is to simply remove the Japanese beetles by hand and dispose of them.
It is getting to be peak Japanese beetle season – mid-summer – so be sure to keep an eye out for skeletonization in your gardens. Early action is crucial to protect your plants, but there are options for management if the Japanese beetles decide that your garden is a good home and buffet.
For more information, check out UGA Extension’s article titled “Japanese Beetles in the Nursery and Landscape” or UKY’s article titled “Japanese Beetles in the Urban Landscape.”
If you have questions and/or comments, you are always welcome to call the office at 770-307-3029, email Alicia Holloway at aholloway@uga.edu, or stop by the Extension office at 90 Lanthier Street, Winder, GA 30680.
Tatumn Behrens is a recent UGA graduate with a degree in entomology. She is currently interning with the ANR Extension agents in both Barrow and Morgan counties.
