How to discourage sowbugs in the garden

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Last Updated: 
August 1, 2006

CORVALLIS – Looking like tiny armadillos, sowbugs and pillbugs inhabit garden soil, dank basements and shady areas of the yard. They feast on decaying plant material and play a role in decomposing organic matter in the garden and compost pile.

And most annoyingly, sowbugs and pillbugs feed on tender seedlings, young roots, flowers and fruits and vegetables laying directly on damp soil.

Sowbugs and pillbugs get blamed for more damage to garden plants than they actually do, said Oregon State University Extension entomologist Glenn Fisher.

"They are deemed guilty by association, as they are often found feeding in decaying or damaged garden produce," said Fisher. "Actually, diseases, slugs and other pests often inflict the initial damage. Sowbugs enter later to take advantage of the feast. They are great opportunists."

Both sowbugs and pillbugs have seven pairs of legs and are dark gray, brown or almost black after molting. The type that curls up in a ball when disturbed is often called pillbugs. True sowbugs cannot curl up in a ball and have two small projections at their hind ends. Both are similar enough in lifestyle to be considered "sowbugs" by most biologists, said Fisher.

Most active at night, sowbugs hide in dark, moist protected areas during the day, such as under flowerpots, decaying leaves on the soil surface, boards, mulches and ground cover. They thrive under sprinkler irrigation. They do no structural damage to homes and will not harm humans or pets.

Fisher recommended some strategies to reduce sowbug populations in the yard and garden.

Limit moist, dark hiding places. Clean up organic debris, boards, boxes and piles of leaves around the yard and garden.

Water early in the day so plants and the soil surface dries out by the evening when sow or pillbugs are active.

Mulch with coarse materials, so water passes through to the soil quickly.

Elevate fruits and vegetables off the ground with old strawberry baskets or pebbles. Black plastic mulches are good because they get too hot in the summer to provide desirable shelter for sowbugs.

Seal cracks around the house and eliminate the dark, damp hiding places next to your foundation if sowbugs are entering your basement.

Plant seeds deeply and do not water until seedlings have their first true leaves. Or start seedlings indoors. Then to maintain good drainage, transplant seedlings into the garden so that the soil around seedlings is higher than surrounding garden soil.

Wheat bran-based slug and snail baits containing carbaryl among the active ingredients will also help control sowbugs. A less toxic method for sowbug control is to place a rolled up newspaper tube on the soil surface. Leave it overnight. In the morning, shake out the tubes into a pail of soapy water.

Another less toxic method to control sowbugs is to sprinkle diatomaceous earth directly on the row where seeds have been planted to dry the soil surface enough to discourage sow bugs. Experiment with the amount of diatomaceous earth, as too thin a layer will not be effective and too thick a layer can become like plaster if it becomes wet.

Author: Carol Savonen
Source: Glenn Fisher