Symphylans

Garden symphylans, also called garden centipedes, are slender, white arthropods, closely related to insects. They are about 0.33 inches (8 mm) long, with 10 to 12 stubs (prolegs) rather than jointed, true legs, and distinct antennae. These fast-moving arthropods live in soil and move up and down in the soil profile, following the moisture gradient. After irrigation, they are near the soil surface. As the soil dries, they move deeper into the soil. They hide when exposed to light. They occur mainly in soil with high organic matter and especially on farms that fertilize with manures. Symphylans can live up to several years. Unable to dig tunnels, they move long distances in the soil profile (up to 3 feet below the soil surface) through existing soil pores. They are hindered in compact soil or sandy soils since these soils lack structure to provide them with adequate tunnels for their movement.

Garden symphylans feed on both decaying and living plant material. They can damage all life stages of a plant, from the seedlings (before or after emergence) to the older plants. They slow plant growth by feeding on root hairs and small roots, which prevents the plant from developing a healthy root system and creates entryways for pathogens. They are less able to injure larger plants. Damage is usually concentrated in relatively small, localized areas of a field, recurring every season. Infestations spread slowly.

This pest usually occurs in relatively small, localized areas of fields, and often in soils with high organic matter.

To prevent damage by symphylans:

• Reduce the amount of compost or manure that is applied to the soil.
• Refrain from seeding until soil-incorporated weeds have broken down.
• Heavily seed problem areas in order to compensate for some probable seedling loss.

Use cultural controls in an organically certified crop.

Research from other areas of the country indicates that symphylans can be detected with bait trapping using carrots or potatoes.

• Cut the carrot or potato in half longitudinally.
• Scratch the cut surface just before placing it in the soil to ensure it is moist.
• Place the bait at a depth where the soil is moist and cover it with a plastic cup to exclude light and prevent the soil from drying out.

Use a minimum of one bait station per ten acres. After 2 to 5 days, examine the cut surface and the soil upon which it was resting for symphylans or evidence of feeding on the bait. If found, consider applying an insecticide. If large numbers are detected (more than 20 per bait station), consider planting the field to a different crop such as wheat, corn, barley, tomato, or oats, which may help suppress populations.

Infested soil can be treated with an insecticide, but its impact may be limited because symphylans have the ability to migrate deep into the soil. Insecticides may help in giving the plants a chance to establish in a protected zone. Apply an insecticide just before planting. Spot treatments may be adequate.