Japanese Beetles in Gardens

P.J. Liesch, UW-Extension entomologist
UW-Madison, College of Agricultural and Life Sciences Department of Entomology
Twitter: @WIBugGuy

3:10 – Total Time

0:17 – What are Japanese beetles
0:55 – Identifying Japanese beetles
1:38 – Protecting plants from Japanese beetles
2:27 – Japanese beetles larvae
2:58 – Lead out


Lorre Kolb: Japanese beetles in gardens. We’re visiting today with P.J. Liesch, Department of Entomology, Insect Diagnostic Lab, University of Wisconsin-Madison/Extension, in the College of Agricultural and Life Sciences, and I’m Lorre Kolb. PJ, tell us about Japanese beetles?

P.J. Liesch: Japanese beetles are a non-native species. They were brought into the U.S. over a hundred years ago and they’ve been in Wisconsin for a couple decades. Every year right around the Fourth of July, the Japanese beetles make their emergence and they can really be active for about six to eight weeks. So the months of July and August they can be very, very active. They can cause damage to several hundred different types of plants, from fruit crop plants to ornamental trees and shrubs. So they really can cause problems for landscapers, and home gardeners, and even farmers, and folks with orchards.

Lorre Kolb: So, how do you know if you have Japanese beetles?

P.J. Liesch: Well, luckily, they’re fairly easy to identify. Japanese beetles themselves are just about a quarter of an inch long. They have distinct coppery brownish wing covers. They’ve got greenish color on the rest of the body and on the sides of their abdomen they’ve got a series of distinct white patches of hairs. If you have had them in the past, you’re almost certainly going to have them again this year, unfortunately. The damage that Japanese beetles cause, we often refer to it as skeletonization. Essentially what the beetles do is they nibble around on the tougher veins on the plant leaves and they focus and feed on the tender leaf material, and it leaves this lace like or skeleton of the leaf behind; that’s classic Japanese beetle.

Lorre Kolb: And what can you do about Japanese beetles?

P.J. Liesch: If you have a few smaller plants and you have the time and you’re at home perhaps, you can actually hand pick and remove the beetles, although that’s going to be very labor intensive and you’d have to do it just about every afternoon. Another alternative, you can cover plants with a fine mesh netting, or similar material, to physically prevent the beetles from getting to the plants and feeding and causing damage. For larger plants, we do have contact insecticides that you can get from the hardware store garden center that can be sprayed. There are also some systemic products that can be applied to the soil, although those products take some time to get moved upwards into the plant. And with any of those insecticide products, you always have to read and follow all the directions very carefully, so that we’re not posing any risk to non-target organisms, such as bees.

Lorre Kolb: What about pre-adult stage?

P.J. Liesch: Females go to low cut, irrigated, turf grass areas and when they go to those areas, they lay eggs, the eggs hatch, and then the larval stage, we refer to as white grubs, they live in the soil and they feed on roots of turf grass. In some cases, we do get damage to home lawns, and golf courses, and cemeteries, sports fields, and very similar turf grass locations. And also, if you have a lot of grubs present, you can get vertebrates in there scavenging on it. So skunks and raccoons can get in there and really churn up that lawn to feed on those grubs.

Lorre Kolb: We’ve been visiting today with P.J. Liesch, Department of Entomology, Insect Diagnostic Lab, University of Wisconsin-Madison/Extension, in the College of Agricultural and Life Sciences and I’m Lorre Kolb.

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