Garden symphylan

About

Not an insect but a small, fast-running soil animal related to centipedes. It is white, about a quarter inch long when grown, with up to 12 pairs of legs (PNW Handbook, UC IPM). The app lists it with insects.

Spotting it

Damage

Symphylans chew sprouting seeds, fine roots and plant parts touching the soil, so seeds fail to come up, seedlings die and older plants are stunted. Damage often shows up in the same patches year after year.

How to find it early

Before planting in spring, dig down to moist soil, set half a potato cut side down on it, cover it, and check after one to three days for small white animals that run from the light. You can also dig up a shovelful of soil and look through it (PNW Handbook).

When

Spring and fall, when they feed near the surface.

Life cycle

Eggs, young and adults are all found in the soil most of the year. In western Oregon they take about 2 to 3 months to mature and can have two generations a year; they move into the top 6 inches of moist soil in spring and fall and go deeper in July and August.

What to do, gentlest first

Start at the top. Sprays are a last step; always read and follow the product label.

1. Till when they are near the surface Prevent

   Tilling crushes symphylans and breaks up the soil pores they travel through; the effect lasts about two to three weeks. Do it right before planting, when they are in the top layer of soil (OSU); UC IPM suggests tilling vigorously while the soil is dry.

2. Choose and rotate crops Prevent

   Potatoes and beans are rarely hurt and can lower numbers, while spinach and mustard build them up. Larger-seeded crops do better than small-seeded ones, and planting squash more thickly helps enough seedlings survive.

3. Firm or flood the soil Prevent

   Rolling or packing the soil after planting can limit their movement, and flooding for about 3 weeks helps where the soil holds water (UC IPM, OSU). OSU also suggests limiting heavy additions of manure and crop residue.

4. Protect natural enemies Natural enemies

   Fungi, predatory mites, ground beetles, centipedes and spiders attack symphylans, though little is known about how much they help (PNW Handbook).

Plants it goes after

Asparagus, Beet, Broccoli, Carrot, Mint, Onion, Spinach, Strawberry, Sweet corn, Winter squash and pumpkin, Zucchini and summer squash

Pressure by region

They infest many home gardens in western Oregon and Washington, mainly moist, well-structured soils rich in organic matter. UC IPM documents damage in California (Santa Cruz County). Ratings outside the Pacific Northwest and California are estimates.

Ratings come from extension sources where available; some are estimates, as noted above.