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The preferred
food source of the Western Corn Rootworm beetle is corn pollen and corn
silks. Adult rootworm feeding on silks has been thought to interfere with
pollination and grain production. The adults prefer to feed on corn, and will eat long, narrow strips in leaves if tassels have not
emerged and pollen is not available as food. Leaf feeding turns a light gray.
Heavily eaten leaves may split and fray in the injured area. Once pollen shed is
completed, they usually migrate in search of other pollen sources, such as
later-planted corn fields or other pollen producing crops.
The first
objective of scouting for rootworm adults is to determine their potential to
interfere with pollination. In commercial field corn, treatment may be justified
if you find five or more beetles per plant, pollination is not complete, and
silk clipping is observed. A second objective of scouting for rootworm beetles is to
determine the potential for rootworm larval injury problems next year, either in
corn after corn or corn after soybeans. The third objective of scouting for
rootworm beetles is to determine whether you should prevent them from laying eggs this
year to prevent rootworm larval injury next year.
A variant of the
Western corn rootworm has adapted to laying eggs in soybean fields, and hence
the emerging rootworm larva will have corn roots to feed upon in most cases, as
a majority of corn acres are in a soybean-corn rotation. Observations and
studies indicate that the problem is expanding. Management
options for rootworms include soil and seed-applied insecticides and utilization of
YieldGard™ Rootworm Bt hybrids. A
primary concern for producers is the damage caused by corn rootworm beetle
larvae as they hatch from eggs in the spring and feed on the roots of corn
plants (see Corn
Rootworm Larvae).
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