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Army Cutworm Alert:  Scout Winter Wheat and Alfalfa Now

                              

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The last time we had a significant army cutworm infestation in SD was in 1998.  Infestations
in 1999-2001 were moderate and less widespread.  Army cutworm infestations of winter
wheat and alfalfa appear to be significant again in 2002.

Winter wheat and alfalfa growers must check their fields for army cutworms as soon as
possible.  Delayed green-up of wheat and alfalfa may be a sign of insect infestation.

Very high numbers of army cutworm larvae are being reported in some western SD counties
at this time.

Clair Stymiest (Crops Specialist at the SDSU West River Extension Center) reported as early
as April 2 of economic infestations of army cutworms on winter wheat near Wall in Pennington
County.  Numbers of as high as 20 larvae per square foot have been detected near Midland in
Haakon County.

Significant numbers (between 2-21 larvae per square foot) of army cutworms have also been
seen on winter wheat in Tripp and Mellette counties.  Bob Fanning (Agronomy Educator,
Lyman County) has inspected several winter wheat fields in the Witten (Tripp County) and
Wood (Mellette County) areas after a grower complained of winter wheat not greening up at
this time.  Bob reported that the army cutworm infestations in south central SD this season
appear to be higher than usual.

Army cutworms also feed on alfalfa.  Marty Philips (Crop Consultant, Crop Tech) has reported
that army cutworms are currently delaying alfalfa green-up near the Winner area.  Populations
of more than 2 per square foot have been detected on alfalfa.

Not all fields will have economic numbers of army cutworm larvae so it is important to quantify
the insect population before deciding to spray the field.  When scouting for larvae, scratch the
soil surface to expose hidden larvae if sampling during the day.  Larvae feed at night and hide
in loose soil clods during the day.

Yield advantages of up to 26% had been recorded in Kansas winter wheat if army cutworm
larvae were sprayed with an insecticide in the spring.  The cost of spraying and the potential
market value of wheat must be considered before spraying the field.

Economic thresholds and insecticides for use on wheat and alfalfa can be found at:

plantsci.sdstate.edu/ent/ecb/army_cutworm_insecticides.htm

Army cutworms are not the same as armyworms.  Army cutworms overwinter as larvae.
They are therefore seen on the field very early in the season.  Armyworms, on the other hand,
do not overwinter in SD.  Armyworm moths do not start migrating into the state until late April
of the current year.  Armyworm larvae are therefore usually not detected until June or July.
The word “army” connotes that the larvae of both insects can move en masse from field to field.

Army cutworm moths start laying eggs in the soil starting in late August of the previous year.
The moths will keep on laying eggs until killed by a hard frost. The eggs hatch immediately
then the larvae start feeding on available plants.  These larvae become inactive when freezing
temperatures set in then overwinter as partially grown larvae.  Army cutworm larvae resume
feeding in the spring of the following year as soon as temperatures exceed 40 degrees.

Mature larvae can reach up to 2 inches in length then pupate in the soil.  Adult "miller" moths
emerge from the soil May to early June, migrate to the Rocky Mountains in the summer to
enter an inactive phase.  Then they come back to the Plains in the fall to lay eggs in the soil.

 Last Updated on Monday, April 15, 2002 by Mike Catangui

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