Every year in our gardens and landscapes, we have unwanted visitors that show up and leave a big mess. They eat just about everything in sight, and leave our plants in bad shape.
Japanese beetles show up about the same time each year, and they stay around for three to four weeks.
Japanese beetles were introduced into the United States in 1916 in New Jersey. Since then, they have spread to all the Northern states, Midwestern states and to the Southern states. In Georgia, they are found north of the fall line. They tend to like heavy soils, such as clay. However, some Japanese beetles have been found south of the fall line. I found my first Japanese beetles in my garden in 1996, and the numbers have steadily increased since then.
Japanese beetles are very striking insects. They are a bright metallic green with coppery brown forewings that reach almost to the tip of the abdomen. There is a row of five white spots along the side of the abdomen and a pair of white spots on the top of the last abdominal segment. These spots help distinguish this beetle from similar beetles, such as the Green June beetle.
Japanese beetles have a preference for what type of plants that they like to eat. Two of the plants that are their favorites are roses and crape myrtles. Other plants that they like to eat are hibiscus, apples, pears, plums and many of the vegetable plants, especially beans.
The damage is very easy to recognize. They eat the tissue between the veins of leaves. They also eat flowers.
If you have blooming plants in the landscape, this is one of the first places to look for them. Besides the adult beetle being a major pest, the larval stage is a plant pest as well. The larval stage, which is a white grub, eats the roots of plants. They are a major pest of turfgrass.
To control Japanese beetles, we must understand their life cycle. There is one generation per year. The adults emerge in late May or June and can be active until July. The adults will live four to six weeks with the females laying eggs during most of their lives. The eggs hatch in two to three weeks. The grubs feed on the roots of plants and will become mature grubs by early fall. The grubs over-winter in the soil, and in the spring they pupate and become adults. Then the cycle begins again.
Controlling Japanese beetles requires controlling the adults and the white grub stage. There are a number of ways to control the adults. First, you can hand pick them when you first see them in your garden. I use a small bucket that has soapy water in it and knock the beetles into the water. Another control option is Bacillus thuringiensis var kurstaki, or Bt.
Bt is a fungus that the beetles eat and then they die from a disease. You can find this in products such as Bt or Dipel.
If you want to use an insecticide, you can use Sevin. If you use Sevin, you need to use it late in the afternoon to reduce the chance of exposing bees to the insecticide. Imidacloprid is another good control option.
To control the grubs, we have two windows when the treatments work best. The first is late August through September. The other time is in March. The grubs are closest to the soil surface at this time. There is an organic control option available: a fungus called milky spore. The fungus in milky spore is Bacillus popilliae. It is available in stores or online. If you use milky spore, it takes two years for the organism to build up in the soil before you get the best results.
There also are insecticides that can control the grubs. These products control other grubs besides Japanese beetles. Some of the products are imidacloprid, trichlorfon, and halofenozide. These can be found in most garden centers. Be sure to read and follow the labels on all pesticide products.
We do not recommend the use of Japanese beetle traps. These traps have sex pheromones in them. They will trap the beetles, but they will draw them to your yard. The beetles can fly in from as far as a quarter of a mile away.
By scouting your yard and starting an early control program, you can have success on controlling the unwanted Japanese beetles.
Columbia County extension agent Charles Phillips can be reached at (706) 868-3413 or by e-mail at email@example.com. The Extension Web address is www.ugaextension.com/columbia.
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