Garden Symphylan

Garden symphylan, also called garden centipede, is closely related to insects. Symphylans are slender, elongate, and white with prominent, long antennae. When full grown, they are 0.5 inch long or less and have 15 body segments and 11 to 12 pairs of legs. They may be found more than 3 feet below the surface of the soil.

Symphylans may damage sprouting seeds, seedlings before or after emergence, or older plants. They feed primarily on root hairs and rootlets. Feeding may stunt transplants as new roots grow out of the transplant plug.

The economic significance of symphylan feeding decreases as plants get larger and older. However, their pitting of roots may provide entry for pathogens, regardless of plant age.

Symphylan damage mainly occurs in well-drained soils with high content of organic matter, and especially in farms that fertilize with manures. Symphylans do not thrive in compacted or sandy soils.

Reduce organic matter input. Monitor where symphylans have previously been a problem to determine the need for spot treatments.

Numerous organisms prey on symphylans, including predatory mites, predaceous ground beetles, true centipedes, and various fungi, but little is known about their effect on symphylan abundance. Consider installing and maintaining insectary plants to attract natural enemies of garden symphylans.

The effectiveness of rotations with nonhost crops has not been studied; however, you can use the following cultural methods to prevent and control damage from garden symphylans:

• Reduce the amount of nondecomposed plant material and manure that is applied to the soil.
• Wait to seed or transplant until the cover crop, soil-incorporated weeds, and manure have completely broken down.
• Pack down the soil surface after planting to reduce crop injury.
• Plant a higher seed population in problem areas to help compensate for damage.

Use cultural control in an organically certified crop.

Visual detection of any symphylans before or at planting often indicates that symphylans are numerous enough to cause economic damage. Bait trapping is a relatively efficient and easy sampling method. Before planting, use bait trapping to monitor garden symphylans by using the procedure described below:

1. Cut raw beets, carrots, or potatoes in half, in the way that exposes the most inside surface area, or in thick slices. Scratch the cut surface immediately before placing it at a depth where moisture is clearly visible in the soil. Use at least one dozen bait traps in a 10- to 15-acre field.

• Remove dry soil from the surface with care; do not disturb the pores in the moist soil, through which symphylans move to reach the bait. Rake the dry soil away with a lettuce knife, rather than slicing into the soil with a knife or spade.

2. Cover each bait trap with a solid plastic cup or small plastic pot.

• Make sure the plastic cap or dome is large enough to prevent excessive heating of the bait or accumulation of excess condensation. A round, white, plastic pot or Styrofoam cup about 6 inches in diameter and 6 inches deep, with no drainage holes, is adequate.

3. After 24 to 36 hours, remove the cover and count the symphylans, first on the soil surface underneath (symphylans will quickly hide), and then on the beet, carrot, or potato slice.

If any symphylans are present on the bait, significant stand loss can occur. Apply insecticide if any symphylans are detected on the bait. This will kill symphylans near the surface and allow the crop to better establish their roots.

Spot treatments with insecticide may be adequate. However, symphylans deeper in soil will eventually reinfest the root zone. If cultural methods and insecticide application are not enough to avoid damage, consider preplant soil fumigation.