Japanese Beetles – Be on the Lookout for this Destructive Pest

Japanese beetles have become a yearly pest. They were first reported in the United States in 1916 and have since become established in many states – including Kansas. The adult beetle is one of the most destructive insect pests we face. I have recently found them attacking my rose bushes and crabapple tree.

The adult beetle is the most troublesome for the homeowner as it feeds on a wide variety of plants including rose, crabapple, birch, grapes and a whole host of other plants. They feed on leaf surfaces and will cause holes and in some cases, they will feed on the leaf tissue between the veins causing a lacelike or skeletonized appearance. However, it is the Japanese beetle larvae that is a major problem in the home lawn, golf courses, athletic fields and other turfgrass locations. They feed on the roots of turfgrass causing the grass to be unable to uptake water and nutrients.

We typically start seeing Japanese beetles in June and they feed through late August. Japanese beetles are 3/8 to ½ inch long. They are metallic green with coppery-brown wing covers and dark green legs. One distinguishing identifier is the white tufts around the abdomen area. These tufts actually look like white dots. The larvae are a white grub that looks very similar to other grubs commonly found in our area. It is actually very hard to tell the difference and would require looking under a microscope.

Japanese beetle adults are active on warm days and prefer feeding on plants that are in full sun. They begin feeding at the top of plants and gradually move down as they consume more and more leaf tissue. Fortunately, most well-established plants can tolerate some feeding damage without causing significant harm to the plant. But the plants will look rather tough after Japanese beetles have worked them over. A light fertilization will help with plant recovery.

The earlier we can implement management of the Japanese beetle, the less plant damage we will see. As for control, there are several routes that can be taken – cultural, physical and insecticidal.

Cultural control includes such things as proper watering, fertilization, mulching, and pruning. Keeping plants healthy will help them tolerate minor infestations better. Weeds should be removed.

Physical control is nothing more than removing the beetles from the plant by hand. The best time to collect beetles is early in the morning or late evening when they are less active. To remove, knock the beetles off by hand into a bucket containing soapy water. The soapy water will kill them. This works fairly well because adult beetles actually fold their legs when disturbed and will fall. Also, Japanese beetles often feed in clusters so knocking them off in masses is easy.

Chemical spray options are available. All plant parts should be thoroughly covered to be most effective. Insecticides including cyfluthrin and bifenthrin can be used. However, they will need to be applied every few weeks during the feeding period. The downfall to using insecticides is the killing of beneficial insects that can actually control other pests such as spider mites.

There are trapping systems on the market but if not used correctly they can actually increase the number of Japanese beetles! The traps contain a lure or scent that draws the beetles to the area. Therefore, they are not recommended.

Now is the time to scout your plants every few days to see if insects have moved in and started feeding. If you have questions or need help identifying a particular insect, please contact me.

Krista Harding is a K-State Research and Extension agent assigned to Southwind District.  She may be reached at kharding@ksu.edu or 620-244-3826.

 

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