Wireworms are not what most gardeners think they are. They are not
the wiry, gray to brown millipedes so often found coiled like a watch-
spring in or near rotting roots. True wireworms have a hard wiry shell,
but they are straight, not coiled, and they have only 3 pairs of legs instead of hundreds (Figure 66A). Wireworms are larvae of click beetles,
those curiously jointed black beetles that snap upright with a clicking
sound when you put them on their backs. The beetle stage lasts for a
year, most of it underground, and the wireworm larvae can live in the
soil 2 to 6 years, moving downward if the upper surface dries out. They
are most injurious to potatoes, beets, carrots, onions, also to corn and
grain crops, sometimes to phlox, asters, gladiolus, and dahlias.
There are many species, but the larvae are usually hard, dark-brown,
smooth, wirelike worms, 1/21 to 11/2 inches long. Adults are brown, gray
or nearly black, about 1/2 inch long, with the body tapering at both ends,
and a special flexible joint between thorax and wing covers. The worms
eat small roots, bore into fleshy roots and underground stems; they also
feed on germinating seed. Young plants are killed, others lack vigor.
Control. Benzene hexachloride has given outstanding control of wireworms but imparts a disagreeable flavor to potatoes and other root crops.
Lindane, the purified form of BHC, is better in this respect but may leave
a slight off-flavor. Aldrin and dieldrin are promising. DDT dusted on
the ground at the rate of 1/2 to 1 pound of 5% dust to 100 square feet
and cultivated in before planting is suggested for small garden plots.