WSU CAHNRS

Washington State University Extension

Garden Tips

WHAT’S THAT BEETLE EATING THE LEAVES OF MY PLANTS?

GARDEN TIPS – Written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Published June 5, 2016

In this area we can consider ourselves lucky that we have not had to deal with the voracious Japanese beetle. This leaf-feeding beetle is the scourge of gardeners in the eastern part of the US where it chows down on hundreds of species of plants. This includes vegetable and fruit crops, flowers, trees, and shrubs. The adult beetles skeletonize leaves by feeding on their upper surface and leaving only veins behind.

So far the Japanese beetle has not become a problem in Washington and the Washington State Department of Agriculture (WSDA) is trying to keep it that way. First, there is a quarantine on plant materials coming into Washington from infested parts of the country. WSDA requires that nursery stock and sod from these areas be inspected and certified to be free of Japanese beetle larvae or adults. That is why gardeners sometimes encounter a mail-order nursery that will not ship plants into our state. These nurseries do not want to take on the expense of getting their plants inspected for selling and shipping to Washington. To ensure that the quarantine is working, every year WSDA monitors areas of the state using Japanese beetle traps.

The rapacious Japanese beetle may not be a problem here, but there are other leaf feeding beetles that can be troublesome in our yards and gardens. The Colorado potato beetle attacks potatoes and its close relatives, including peppers, tomatoes, and petunias. When the Colorado potato beetle is present, there is no mistaking it. It is almost .5 inch long and .25 inch wide with a reddish head and a tannish-yellow and black-striped body. It damages potatoes by eating holes of varying sizes in the leaves, as well as feeding on leaf edges. Severe infestations can cause significant damage.

Those gardeners not wanting to utilize chemicals for control can try the “hands-on” approach by looking for and squishing any clusters of bright yellow eggs found on undersurface of the leaves and any adults and orange-red larvae found on the top of the leaves. Remove weeds in and around the garden because they may be serving as alternative food sources.

There are chemicals available for Colorado potato beetle management. These are most effective when applied as soon as the beetles are first discovered and again if needed. Be sure to treat the bases of the vine stems along with the leaves. (For chemical options go to WSU’s Hortsense website at http://hortsense.cahnrs.wsu.edu.)

Yet another leaf-feeding beetle can be a problem for area gardeners. Elm leaf beetles are only about .25 inch long with yellow-green and olive-green striped bodies. These guys and their yellow to green larvae feed on the undersurface of elm leaves, leaving the veins and the waxy upper surface of the leaves behind. In certain years these beetles are numerous and can effectively defoliate a tree. If this happens early in the season for several consecutive years it will stress and weaken a tree and possibly lead to its death. Luckily, the Elm leaf beetle population goes in cycles with high numbers some years and lower numbers other years.

It is difficult to control this beetle because its damage is often not noticed until after it has occurred. While there are chemicals available for management, a commercial pesticide applicator should be hired if the tree is above 10 feet tall. There are also systemic insecticide drenches that can be applied to the base of the trunk, but they should be applied prior to the appearance of the beetle damage.

Garden Tips, WSU Extension, Benton County, 5600-E West Canal Drive, Kennewick, WA 99336-1387, 509-735-3551, Contact Us

WSU Extension, Franklin County, 1016 North 4th Ave, Pasco, WA 99301-3706, 509-545-3511, Contact Us
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