submitted by Michelle Gobert, Master Gardener
Recently, our office has recently fielded several questions regarding turfgrass damage, as well as concerns for raspberry and blackberry plants flowering but not producing and while there may be several reasons for both types of damage, they both have one thing in common and that is a white grub infestation from either the Japanese Beetle or May/June Beetle.
Description of the Japanese Beetle
According to an article published by Wisconsin Horticulture authors R. Chris Williamson, PJ LIesch and Vijai Pandian of UW-Madison Extension, the Japanese beetle is a “significant pest of landscape trees and shrubs, vegetable and fruit crops, and turfgrass in the eastern United States.” It is a non-native species that was first discovered in the U.S. in 1916.
Japanese beetle adults are a shiny, metallic-green and slightly less than ½ inch long. They have coppery-brown wing covers (elytra) that rest on their backs. At the edges of their backs are small patches of white hairs. Males and females look similar, but females tend to be slightly larger. Newly hatched larvae (white grubs) are C-shaped, approximately ⅛ inch long with pale bodies; mature grubs are up to one inch long.
Description of May/June Beetle
According to P.J. Liesch of the UW-Madison Entomology lab, May/June beetles (sometimes called “Junebugs” are native insects that are common throughout Wisconsin, with twenty-nine documented species in Wisconsin, and over 200 species in North America.
Adult May/June beetles are typically ½ to one inch long and vary in color from reddish-brown to almost black. Adults are active after dusk in late May and early June and are attracted to lights at night. These insects are clumsy fliers and often collide with windows and cling to screens. Immature May/June beetles (i.e., larvae or “white grubs”) have distinctly C-shaped, cream-colored bodies with a reddish-brown head and three pairs of legs. Grubs can be up to 1¼ inches long, and live in the soil using their strong mandibles (i.e., mouth parts) to chew on plant roots.
Plants attacked and the Damage Done
The adult Japanese Beetle is known to cause leaf and flower damage of over 350 species of fruits, vegetables, ornamentals, field and forage crops and weed. The adults feed on the upper surfaces of leaves of these plants, consuming soft tissues between the veins, and leaving behind a lace-like skeleton leaf. Trees with extensive damage turn brown and drop their leaves.
In comparison, the May/June beetle are pests of turfgrass, ornamental plants, Christmas trees, cranberries and certain vegetable and field crops. Adults have been documented to cause leaf damage to these plants, although this type of damage according to P.J. Liesch “occurs infrequently and tends to be localized in the state”.
Larvae (grub) stage
In both cases, it is the beetle larvae (white grub) stage that most likely is causing damage to the turfgrass, as well as the raspberry and blackberry plants in our area although the only way to know for sure is to capture the grubs and send them into the state bug lab for identification.
White grubs of both the Japanese Beetle and the May/June Beetle, damage plants by feeding on their roots and disrupting the update and transport of water and nutrients. Initial symptoms of grub damage appear similar to those of drought stress including the yellowing and wilting of foliage, as well as the stunting of plants. When high populations of grubs occur in turfgrass, discoloration of loosely rooted turf can appear in mid-to-late summer. Damage from these grubs can occur anywhere in Wisconsin but is most commonly found in the eastern and northeastern parts of the state.
Secondary damage to turfgrass can be significant and occurs as animals such as skunks, raccoons, turkeys and sandhill cranes dig and forage for grubs.
Grub Identification and Control
As stated above, the only way to know for sure what beetle is causing grub problems is to have the grub identified by the state entomology lab. Last month, a local resident did request this service through the Extension office, and the May/June beetle appears to be the culprit in this particular case. Knowing what beetle you are dealing with will allow you to take the next steps to control the problem.
If you are interested in submitting a sample to the state lab, please contact the Extension office at 715-478-7797. Once identified, control of white grubs can involve use of non-chemical, chemical and biological methods or a combination of methods. In-depth information is available in the article titled “White Grub Control in Turfgrass” authored by PJ Liesch and Vijai Pandian of UW-Madison Extension.
For more information about the programs and services of UW-Madison Division of Extension Forest County, please visit our website at https://forest.extension.wisc.edu or call our office at 715-478-7797.
