The Japanese beetles will soon be out in full force. They are in west Georgia and will begin emerging here soon. They are a huge pest as they munch their way through your yard. Controlling them can be challenging because they are such voracious eaters. Let’s talk about some strategies for lessening their impact.
Japanese beetles arrived in the U.S. 1916. They have spread to much of the East coast and across the Mississippi River. They will feed on a wide range of ornamentals, fruit trees, vegetables, and shade trees. Feeding on such a wide range of plants means that your yard may look like an all you can eat buffet to them. They have a metallic green color on their abdomen. They look similar to June beetles. June beetles are typically about 1.5 to twice as large as Japanese beetles. Japanese beetles also have a row of five white dots along the side of the abdomen that can be used to differentiate them from other beetles. The damage that you see from them looks like skeletonizing of the leaves. They’ll eat everything between the leaf vein, but leave the veins.
Thankfully, Japanese beetles only have a single generation each year. Usually the adults, which are the beetles that we see flying around eating leaves, will begin to appear in May – June . They live four to six weeks. The females will lay eggs for most of their adult life. The eggs are laid in the soil. They hatch in about two weeks. After hatching, the beetles live in the soil until they come back out as adults in May.
There are three times a year that are most ideal for controlling Japanese beetles. The most obvious is when they are adults and are out feeding on leaves. You can use carbaryl, which is the active ingredient in Sevin to control adults. Sevin comes as a liquid or in dust form. If you don’t have a heavy infestation you can also use a cup with soapy water in it. Knock Japanese beetles off plants into the cup and they will drown. The second time to control Japanese beetles is in September. By that time of year all the Japanese beetles are grubs living in the soil. Even as grubs they can do damage to turf by feeding on the roots. Milky spore is an organic product that can be used to kill grubs in the ground. It’s a bacteria that feeds on Japanese beetle grubs after they ingest it. September is the optimal time to make a milky spore application. The third time to control Japanese beetles would be in the spring with another milky spore application. Soil temperatures need to be over 65 for milky spore to be effective. The grubs must ingest the milky spore for it to be work. It only works on grubs, so applying it while the beetles are out eating leaves won’t kill any Japanese beetles.
Using milky spore to kill the grubs doesn’t mean that you won’t have any Japanese beetles the following year, but you can significantly reduce the population that is present in your area. Some people will use traps to kill Japanese beetles. I try to discourage people from this practice because traps with pheromone lures will bring beetles in from five miles away, meaning that you have more beetles.
If you have questions about Japanese beetles contact your county Extension Office or email me at Jacob.Williams@uga.edu.