If you have medium to heavy, clay soil, your problem may have been tiny soil-borne pests called garden symphylans. Symphylans feed on germinating vegetable seeds, roots and plant parts in contact with the soil. They stunt older plants by poking numerous small, shallow holes in root crops. Rarely seen, pale-colored symphylans live in the soil, or under organic material on the soil surface, according to Ralph Berry, professor of entomology at Oregon State University and Ed Peachey, OSU horticultural researcher. Too weak to make their own tunnels or runways in the soil, tiny symphylans, travel via earthworm burrows, soil cracks and the paths made by other soil creatures.
Large numbers can cluster in a small area.
They hate the light. Symphylans also eat fine root hairs, thereby interfering with water and nutrient absorption. Surviving plants produce poorly, are more susceptible to infection, mature unevenly and are smaller than healthy plants. Yields are lower, and fruit and vegetable maturity is delayed in home gardens as well as commercial greenhouses, nurseries and farm fields. They prefer heavy clay soils like those in the Willamette Valley because invertebrate burrows stay intact, said Berry.