How to Manage Pests

UC Pest Management Guidelines

Garden symphylans are slender, white arthropods, closely related to insects, about 0.33 inch (8 mm long), with 10 to 12 prolegs and distinct antennae. These fast-moving arthropods live in soil and move up and down in the soil profile with the moisture. They run when exposed to light. They occur mainly in soil with high organic matter and can cause considerable damage in asparagus plantings.

Garden symphylans cause injury by chewing large numbers of small, round holes in storage roots, crowns, and on the belowground portion of the spears. They also predispose the asparagus plants to additional damage from disease organisms (Fusarium, Phytophthora, etc.) that invade the wounds they create. The insects are a particular problem during periods of extended wet weather in northern California production areas, primarily the Delta, or on water-saturated soils. A good indication that these insects are present is circular areas in the field or along edges of the field in which there is little or no asparagus or weed growth.

The practice of mounding soil against the spears to produce white asparagus increases the damage potential of this pest. Since the demise of the white asparagus industry in California, crop loss has been reduced.

Before planting asparagus, flood selected fields during summer when they are fallow. Complete coverage of the field is essential for good control. Hold the water on the ground for 1 to 2 weeks during the warmest portion of the summer. On existing fields already planted to asparagus, winter flooding of the fields for a period of 2 to 3 weeks when the crop is dormant has helped to reduce damage in affected areas. Additionally, cultivation to dry out the surface soil of the beds has reduced injury by driving the insects deeper into the soil.

Research from other areas of the country indicates that symphylans can be detected with bait trapping. Either carrots or potatoes can be used as bait. Cut the bait in half longitudinally and scratch the cut surface just before placing it on the soil to ensure that the surface is moist. Cover the bait with a pot. Use at least a dozen bait traps in the field. After 2 to 5 days, examine the cut surface and the soil upon which it was resting for evidence of symphylans. If they are detected, consider a treatment. If large numbers are detected (more than 20 per bait station), consider preplant fumigation or planting the field to a different crop. Because symphylans are likely to occur in the same areas over many years, the loss from these pests is very difficult to manage in permanent crops like asparagus.

Organically Acceptable Methods
Flooding fields before planting or in winter and cultivation are both organically acceptable control strategies.

PUBLICATION

UC IPM Pest Management Guidelines: Asparagus
UC ANR Publication 3435
Insects
W. E. Chaney, UC Cooperative Extension, Monterey Co.
E. T. Natwick, UC Cooperative Extension, Imperial Co.
C. B. Fouche, UC Cooperative Extension, San Joaquin Co.
Acknowledgment for contributions to the insects section:
R. J. Mullen, UC Cooperative Extension, San Joaquin Co.

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