Just about every year, we will get reports of True
Armyworm, Pseudaletia unipuncta,
damage somewhere in the state. Some years, like in 2001 or 2007,
we can have severe outbreaks across a wide region. In most years,
there will be isolated cases but even those can be significant to the
farm affected. Crops most affected are grasses including
field corn, grass hay and pasture crops.
It is important for farmers and consultants to be
monitoring fields starting in mid-June. At a high enough
population, armyworms can create a lot of damage very quickly.
One comment I got from a farmer in 2007 went something
like this, "We looked one day and saw a little damage, but when we
couple days later many of the plants were totally stripped!"
If you detect a problem, try to assess the severity of the damage as well as the age/size and population of the larvae. Spraying with an insecticide is expensive and may not be necessary (or too late).
The best time to look for the larvae is very early in the
morning or just before dark. Armyworm larvae tend to stay near
the soil surface during the day when it is hot and feed at night.
For more information refer to the links and factsheets below:
Armyworm Factsheet (updated with insecticides approved for Vermont in 2017)
Recovery of Field Corn, Haycrops, and Pasture Following Armyworm Damage
What about Bt traits for corn hybrids?
A large number of corn producers use Bt traits in their corn
hybrids; however, the ability to resist armyworm damage varies a lot
from one trait to another and most Bt traits are not affective for tury
armyworm. Michigan State has produce The Handy Table Bt Table for U.S. Corn Production which details which insects are effectively controlled by each trait.
This site is maintained by Sid.Bosworth@uvm.edu,
Plant & Soil Science Department, University of Vermont.
Issued in furtherance of Cooperative
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United States Department of Agriculture. University of Vermont Extension,
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