Doug Johnson,
Extension Entomologist
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Fig. 1. Black cutworm moth.
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Capture
of black cutworm moths in the IPM traps has been above the rolling five year
average for the last several weeks. The activity of this insect has been
notoriously difficult to predict over the years, even with years of data on
its’ flight activity. Nevertheless given that the moth capture is above
“normal” and we are experiencing unusually cool and damp weather, it may be
that we should keep a closer check on our young corn plants.
Corn products that
have the latest edition of “B.t.” traits, will be afforded quite a bit of
protection from this pest. However, corn that does not contain “B.t.” or that
contains only the1st generation “corn borer B.t.” traits will be at greater
risk, if an economically important population occurs. Our traps are unlikely to
provide a definitive warning, so scouting for the damaging caterpillars is the
best way to insure that major loss will not occur.
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Fig. 2. Black cutworm larva |
Cutworm larvae are light grey to
nearly black and may have a faint, narrow mid-dorsal stripe. Larvae vary from
¼” long after hatch to 1-3/4” when full grown. Larger larvae tend to curve
themselves into a “C” shape around the plant and wiggle vigorously when
handled. Damage symptoms are cut or wilted plants.
Scouting should begin from a randomly selected starting
point. Examine 20 consecutive plants per location and record the number of cut
plants. This should be done at multiple locations (at least five) in the field.
Determine the percent cut plants by dividing the total number of plants cut by
the total number of plants inspected and multiply by 100.
If an average of 3% cut plants and 2 or more
live cutworm 1” or smaller per 100 plants examined are found, a control should
be considered. Remember if you cannot find live larvae, the population may have
already completed a generation and control is not warranted
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