White Grubs Thrive on Soybean Roots

May 14, 2019

While seedcorn maggots tunnel through the cotelydons, shoots and roots, another serious soybean pest will eat roots entirely. The larval stage of June beetle, European chafer and Japanese beetle, called a white grub, does just that.

These pests overwinter as larvae in the soil below the frost line. In April to mid-May, the larvae migrates closer to the soil surface where they feed on the seed as well as the seedling’s fibrous roots. This causes the plant to become stunted and wilted, contributing to non-uniform and poor stands.

Three species to watch for

Abhi Deora, Seedcare Technical Lead at Syngenta explains that the species of white grub can be tricky to identify at the larval stage. “They look practically the same, but you can tell them apart by closely looking at the pattern of the bristles or rasters on the underside of their body,” he says. Their life cycles differ, too. “June beetles have a life cycle that spans three to four years and are often referred as ‘true grubs,’ whereas European chafer and Japanese beetle have a life cycle of only one year and therefore are called ‘annual grubs.’”

June beetle and European chafer larvae are more damaging to soybeans compared to Japanese beetle larvae. After overwintering, the higher instar larvae actively look for food sources and affect plant stand. These grubs are more problematic in soybeans if the fields were previously in hay, pasture, sod or cover crops, or in fields which had late-season weed problems the previous year.

closeup of a white grub

Image: European chafer larvae. The larvae are C-shaped and white with a light-brown head capsule. When mature, European chafer larvae have three pair of visible legs and are about ¾ inch long.

Management tips

Scout for white grubs in the fall and spring
Plant crop into ideal soil conditions so that the crop will rapidly become established and able to tolerate low to moderate grub feeding

Protect your soybeans from below-ground feeding

Early-season protection against pests like white grubs is critical to give your soybeans a strong start. Fortenza^® is a new non-neonicotinoid soybean seed treatment that is applied as a commercial seed treatment, and that protects soybean seeds and seedlings from below-ground insect feeding. It’s formulated with cyantraniliprole (Group 28 insecticide) for control of seedcorn maggot, European chafer, June beetle larvae and wireworm. Even under heavy insect pressure, Fortenza helps producers build a strong soybean stand with faster, more uniform growth.

What other pests could be lurking below ground in your soybean field and putting your young crop at risk? Watch for more articles on seedcorn maggot and wireworms to get to know these damaging pests and plan your defence.