Symphylans
(Scutigerella immaculata)
Insects & Invertebrates
Symptoms
Garden symphylans are an occasional pest, but can cause extensive crop damage when present. They live in the soil and feed on fine roots, which reduces the crop’s ability to take up water and nutrients, leading to general stunting. They are exceptionally injurious to young plants. The symptoms of low vigor and weak growth are usually seen between April and June.
Identification
Garden symphylans are not insects but are closely related to centipedes and millipedes. They are white, slender and fragile, about ¼” long with a distinct head. They have between 6 and 12 pairs of legs depending on the age of the symphlans; newly emerged nymphs have 6 pairs of legs and fully mature adults have 12 pairs of legs.
Life History
Eggs are deposited starting in the spring and through the summer; they are deposited in groups of 20 and are white and spherical with hexagonal ridges. Length of egg incubation ranges from 12 to 40 days, depending on temperature. Total time from egg to sexually mature adult (seventh instar) is approximately five months at 50°F, decreasing to approximately three months at 70°F and less than two months at 77°F. It is possible to have two complete generations a year at higher soil temperatures. All life stages are found in the soil. Unlike earthworms, they are not able to burrow through the soil and must use existing pores and cracks to move around.
Monitoring
Symphylans are generally found in the top 10 to 12 inches of the soil, but can penetrate deeper to find more suitable conditions. They are extremely fast moving and run from light so they are hard to find. In the hottest interior valleys, symphylans may be more active in the spring/early summer and the fall, with surface activity dropping off in July, August, and into September. Sample the soil to depth of about 12 inches in each acre of the field and count the number of symphylans present.
Symphylans can be baited for monitoring purposes. A potato or carrot can be cut in half and placed cut side down on the ground with a white plastic pot without holes covering the bait. After 2-3 days the cut side of the bait should be checked for symphylans.
Monitoring counts may vary widely throughout a field. Taking many samples through a field will give a better picture of locations of hotspots.
Management
More than 5 symphylans per shovelful can indicate a problem although thresholds are not well established. Remove affected plants. Soil fumigation can be done in infected fields prior to planting. Spot treatments may be effective.
Tillage can provide some control. To be most effective, tillage should be done when symphylans are in the upper portion of the soil.
Web Resources
Pennsylvania State University, Entomological Notes, Garden Symphylan As A Pest of Field Crops
http://www.ento.psu.edu/extension/factsheets/garden_symphylan.htm
University of California, IPM Online, Cole Crops Garden Symphylans
http://www.ipm.ucdavis.edu/PMG/r108500111.html
WSU Extension Bulletin 1351, Garden Symphylan: Biology and Control
http://cru.cahe.wsu.edu/CEPublications/eb1351/eb1351.pdf
ATTRA, Symphylans: Soil Pest Management Options
http://attra.ncat.org/attra-pub/symphylans.html
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