Description and Biology:
Several species of wireworms attack planted sorghum seed. True wireworms
are immature stages of click beetles, family Elateridae. False wireworms
are immature darkling beetles, family Tenebrionidae. Wireworms are shiny,
slender, cylindrical, smooth, and hard-bodied larvae ranging in color
from white to yellow to brown, and are about 25 mm long when grown. The
last segment of the larva usually is ornamented.
All life stages of wireworms except the adult develop in the soil. Depending
on the species, a generation is completed in one, two, or more years.
Wireworms usually overwinter in the damaging larval stage and are present
in the soil at the time sorghum seed are planted in the spring.
Monitoring: Soil in fields should be inspected for wireworms
before sorghum is planted. However, visually locating wireworms in soil
is difficult. Wireworm abundance can be assessed by placing about 300
g of nontreated sorghum seed in a 12-cm-wide hole at least 10 cm deep,
deep enough to reach moist soil. After covering the hole with soil, the
baited trap should be covered with a 1-m2 sheet of black plastic that
warms the soil and attracts wireworms to the warmed soil and grain. The
trap should be marked with a stake. One trap per each 2.5 to 5 hectares
of field should be installed at least two weeks before planting. Grain
in the trap should be examined two weeks after placement and wireworms
counted. Two or more wireworm larvae per trap are sufficient to cause
stand loss and justify the use of insecticide, especially if conditions
are not good for rapid seed germination.
Management: The amount of damage to sorghum depends on the number of wireworms
in the field at the time of planting and the length of time seed are in
the soil before they germinate. The seedbed should be prepared properly
and seed planted at a time to ensure rapid seed germination. Sorghum should
be planted in a field where a nongrass crop was grown the previous year.
Also, tillage before planting reduces noncrop plants in the field. Insecticide
applied to seed or in the planter-box usually is effective in controlling
wireworms. Seed may be purchased already treated with a systemic insecticide
that protects against wireworms. In-furrow insecticide applications also
control wireworms. When wireworms are abundant, seed treatment should
be supplemented with a granular or liquid insecticide applied to soil
at planting.