Pillbugs were found damaging a field of emerging soybeans north of Fairbury this week. This field was planted around May 1 following corn in 2009, and was in a no-till corn-soybean rotation, except for two years of corn four-five years ago.

Damage was heaviest under corn residue, but also was observed in areas without heavy residue. Feeding damage was most commonly found on the hypocotyls, but also was seen on the cotyledon and on the roots down to 1.5 inches below ground. About two-thirds of the damaged plants were severed. Replant will be necessary in at least part of this field.

Pillbugs are land-dwelling crustaceans, more closely related to crabs, shrimps, and lobsters than insects. Pillbugs are wingless, hard-shelled, gray to black in color and have seven pairs of legs. They are about 3/8 inch long at maturity. They prefer to live in areas with high humidity and moisture, and frequently can be found in areas with organic residue (crop residue, wood mulch, under boards, etc.). They normally feed on decaying organic matter, but occasionally have been reported damaging crops or garden plants.

Typically, less damage would be expected in a replant situation. The soybeans will germinate and emerge more quickly at this time of year, and as temperatures increase, and hopefully things dry out, the pillbugs will be less active at the soil surface. KSU entomologists state “Foliar application of labeled insecticides also has not proven effective” because the pillbugs are protected underneath crop residue.

For more information see, Pillbugs (MF-2855), by R. J. Whitworth, P. Sloderbeck, and H. Davis and published by Kansas State University.

Thanks to Mike Holtmeier, Pioneer Hi-Bred Int., and Randy Pryor, UNL Extension Educator in Saline County, for reporting this situation.

Robert Wright
Extension Entomologist, Lincoln