Sowbugs and pillbugs congregate in moist areas. Photo by Sinclair Adam.
Sowbugs and pillbugs are closely related, but they are not insects. Rather, these arthropods are crustaceans, more closely related to shrimp and crayfish. In fact, they are the only crustaceans that have adapted to living their entire lives on land.
Both sowbugs and pillbugs are oval in shape, with segmented, hard-shelled, grey bodies measuring 1/2 to 3/4 of an inch long. Sowbugs have two small tail-like appendages at the rear, and pillbugs do not. Pillbugs can roll up into balls ("rolly pollies") but sowbugs cannot.
Sowbugs and pillbugs feed primarily on decaying organic matter but are also known to feed on seedling roots and young stems in contact with soil or growing media in greenhouses. We have also seen outbreaks in high tunnels where high rates of compost have been applied to in-ground production beds. Crop losses can be very high due to feeding damage on small seedlings.
Because sowbugs and pillbugs regulate moisture loss poorly, they do not like to be in dry spots, but prefer a moist environment. Persistent, cloudy weather may contribute to sowbug and pillbug outbreaks.
The first step in an IPM approach to managing these pests in the greenhouse is taking away the moisture they need to survive. As much as possible, eliminate protected areas where moisture gets trapped, including under pots, flats, bags of media, or other items stacked on floors, cracks and crevices in walkways, and leaky hoses and faucets. Also, clean up spilled media and plant residues to reduce food sources.
When outbreaks do occur, one approach to controlling these pests is spreading diatomaceous earth on floors or walkways. Be very careful to use the appropriate PPE when using diatomaceous earth to avoid inhalation exposure. A number of insecticides can also be effective (e.g. cyfluthrin, bifenthrin, carbaryl, cypermethrin, permethrin, lambda-cyholothrin). Check pesticide labels carefully and follow all label directions.