True White Grubs in Soybean
Crop Damage
True white grubs are a group of insects (Phyllophaga spp.) found throughout the world. They are the larval stage of May or June beetles and are considered a sporadic soybean pest. Larvae feed on small lateral soybean roots, reducing the plant’s ability to take up water and nutrients. Affected seedlings become discolored, wilt, and may eventually die.
True white grubs.
Clemson University-USDA Cooperative Extension, Bugwood.org
Pest Description
Full-grown larvae (grubs) are approximately 1¼ inches long and have a characteristic C-shaped body with three distinct pairs of orange legs. They have a dark orange-brown head, a cream-colored body, and an enlarged gray area at the end of the abdomen. A key identifying characteristic is the presence of two parallel lines of hairs at the end of the abdomen, known as the raster or “zipper.” Adults are about 1 inch long and are dark red-brown beetles with small hairs on the underside of the thorax. As their name suggests, June beetles emerge in late spring or early summer.
Blue arrows indicate the raster-zipper.
Adam Sisson, Iowa State University
June beetle. Blue arrow indicates small hairs on thorax.
Laura Iles, Iowa State University
Scouting and Management
Grubs are attracted to fields previously in pasture or grasses and to areas near trees. True white grubs are more prevalent during cool, wet conditions when soybean germination and emergence are slow. They have a three-year life cycle, allowing larvae to persist in fields for multiple seasons.
Prior to Planting
Sample grassy areas within and around fields. Dig a one-foot cubic area and search for larvae.
After Planting
Dig up areas with poor emergence or with wilted or dead plants and inspect for white grubs, as several early-season pests can cause similar symptoms.
If one or more grubs are found during pre-season sampling, consider insecticide management options. There are no rescue treatments for true white grubs after planting. Where true white grubs are a persistent problem, delay planting until conditions favor rapid germination and emergence and consider the use of seed-applied insecticides. Management can be challenging because larvae live in the soil and can cause injury during the second year of their life cycle, also known as the second spring larval stage.
Please contact your local agronomist or extension specialist for management information.
Prepared and reviewed by Carol Pilcher and Robert Wright, with support from the United Soybean Board.
True white grubs on soil. Clemson University-USDA Cooperative Extension, Bugwood.org
True white grub. Adam Sisson, Iowa State University.
True white grubs. Blue arrows indicate the raster-zipper. Adam Sisson, Iowa State University.
June beetle. Blue arrow indicates small hairs on thorax. Laura Iles, Iowa State University.
Gallery Images courtesy of Clemson University-USDA Cooperative Extension, Bugwood.org, Adam Sisson, and Laura Iles, Iowa State University.
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