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Small Corn Rootworm Larvae
feed on root hairs and small roots; larger rootworm larvae feed on primary
roots. Both the western corn rootworm (WCR) and the northern corn rootworm (NCR)
attack corn roots. The adult NCR has uniform light green wing covers, while WCR
has black or black and yellow wing covers.
Rootworms overwinter in the egg stage. Eggs start
to hatch in late spring. The date depends on soil temperature. Late May to
mid-June are normal. After hatching, the
small rootworm larvae move to nearby corn roots and begin feeding on root hairs
and small roots. Larger rootworms feed on, and tunnel in, primary roots.
Under heavy rootworm pressure, root systems can
be completely destroyed, but damage usually is less. Yield losses due
to rootworm feeding are difficult to determine, as many corn varieties can
compensate for some root damage. In general, economic losses occur after one or
more primary roots are chewed to within 1.5 inches of the plant. Rootworm damage
also can result in extensive "gooseneck" lodging and harvest
difficulties.
By mid-July, most larvae have finished feeding
and transformed into adult beetles. They emerge from the soil to feed, mate and
lay eggs. These eggs produce the larvae that will attack the following year's
crop.
(see Northern
Corn Rootworm or Western
Corn Rootworm)
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