Crop Scene Investigation - 9 Solved: What had been feasting on Matt's corn roots?

Monday, March 31, 2008

by MIKE FOLKARD

European chafer (white grub) was the pest that vanished after feasting on the roots in Matt's cornfield. The chafers couldn't be found because they had already moved on to the next stage of their life cycle.

European chafers overwinter in the soil below the frost line. During the early part of the growing season, the larvae move up to the surface and feed on the corn plants fibrous roots. When they finish feeding by mid-June, these pests pupate and emerge from the soil as beetles and fly away to mate. In Matt's field, they left behind some key pieces of evidence - the little holes where they emerged from the soil and the skin they shed during pupation.

Typically, when I come across chafer damage, I find larvae lurking in the soil. In this case, I was too late. The white, C-shaped larvae with orange-brown heads and dark posteriors had already matured into medium-sized, light-brown beetles that closely resemble the native June beetle. There is one generation of European chafers per year.

While it's difficult to anticipate a chafer problem, fall scouting is a valuable prevention tool. Newly hatched chafers begin feeding on roots in late July until the ground freezes. So scout on the sandier knolls of the field and dig down about one foot. Avoid planting corn if the population is extreme.

Two or more larvae per square foot indicate the need for control using soil-applied insecticide or seed treatment.

Congratulations to Tom Cox, Troy, for his correct answer. BF

Mike Folkard, CCA, is a field agronomist for NK Brand, Syngenta Seeds. He is based near Belmont.