No. 12/June 12, 1998
Is It Possible That Garden Symphylans
Are Out There, Too?
Mike Porter and John Thieme with Zeneca Ag Products visited a cornfield in Stephenson County in northwestern Illinois that apparently was infested with symphylans. They found a range of 5 to 35 per plant. If this strikes you as unusual, you're not alone. In my 19 years in Illinois, I have observed symphylans in only one field. However, my predecessors observed fields infested with garden symphylans more frequently; we have slides to prove it! I guess in the unusual "insect year" we have experienced thus far, anything is possible.
Figure 4. Garden symphylan adult (actual size is about 1/4 inch).
Garden symphylans, also known as garden centipedes, are neither centipedes nor insects. Adults are small and white, measuring 1/4 inch long, with 12 pairs of legs (Figure 4). Immatures are similar in appearance to adults but have only six pairs of legs. Garden symphylans are infrequent pests of corn and occur most often in fields with sandy loam soil and a high level of organic matter, on which they feed. Damage often is spotty within a field. When densities reach 50 to 100 individuals per plant, garden symphylans can injure corn early in the growing season by feeding on the root system, often stripping off root hairs. Injured plants are stunted and purple. (Oh boy, yet another problem that causes "purple corn.")
Like most other subterranean insects and insect relatives, garden symphylans cannot be controlled with "rescue" treatments. Several soil insecticides have symphylans on their labels, but use of insecticides at or before planting to control symphylans is rarely justified. As we have suggested for grape colaspis problems, if good growing conditions prevail, the corn will be just fine.
Kevin Steffey (firstname.lastname@example.org), Extension Entomology, (217)333-6652