Field Corn

Identification (and life cycle/seasonal history)

Mature larvae are 25 to 40 millimeters (one to ? inches) in length, smooth bodied, and dark gray to greenish black.  They are characterized by five stripes, three on the back and two on the sides, running the length of the body.  While the stripes on the back are variable in color, the stripes on the sides are pale orange with a white outline.  The head is marked with a netlike pattern of black markings.

The armyworm is unable to survive our winters, and armyworm moths migrate into the region in early summer.  They lay their eggs in rows or clusters on the lower leaves of various grass crops.  Dense grassy vegetation is preferred for oviposition.  Newly hatched larvae move with a looping (inch-worm) action.  Larvae feed at night and on cloudy days, hiding under crop debris during sunny periods.  One or more generations may occur per year.

Plant Response and Damage

Armyworm feeding is mostly limited to grasses, although this insect will feed on a number of other plants when starving.  In Colorado, armyworm is mostly a pest of corn and spring grains. In corn, larvae may later enter the ear tip.

Management Approaches

Chemical Control

Armyworms migrate in to corn from grasses or onto corn within grassy cornfields.  They are mostly a problem later in the season.  They feed on the corn plant from the bottom leaves upward.  If the lower third of the foliage is consumed before hard dent stage, chemical control may be justified.  It is unknown if control can be expected with Bt corn hybrids.

 

Product list for Armyworm:
Pesticide	Product/Acre  (Fl oz. or oz. product)	Preharvest Interval, remarks
Asana XLR,1	5.8 - 9.6	21 days.  Apply as necessary to maintain control.  Extremely Hazardous to Bees!
Baythroid XLR,1	1.6 - 2.8	21 days.  See labels.  Extremely Hazardous to Bees!
bifenthrinR,1,2	2.1 - 6.4	30 days.   Use rates below 5.12 fl. oz. only if spider mites are NOT a concern.  Extremely Hazardous to Bees!
carbaryl1,2	See labels	48 days grain and stover, 14 days silage. Extremely Hazardous to Bees!
chlorpyrifos 4ER1,2	16 - 32	35 days.  14 days grazing.  Not for use on popcorn. Extremely Hazardous to Bees!
CobaltR1	13 - 26	21 days.  14 days to graze.  Extremely Hazardous to Bees!
Delta Gold R,1	1.5 - 1.9	21 days to harvest grain or fodder.  12 days to forage.  Do not apply more than 0.095 lb ai/acre/crop.  Extremely Hazardous to Bees!
HeroR,1	4.0 - 10.3	30 days to harvest grain or fodder.  60 days to forage.  Do not apply more than 0.4 lb ai/acre/crop.  Extremely Hazardous to Bees!
Intrepid 2F	4 - 8	21 days. 64 oz per season maximum.  See label for timing information and crop rotation restrictions.
lambda cyhalothrinR,1,2	2.56 - 3.84	21 days.  Apply as required by scouting or locally prescribed corn growth stages.  Do not apply more than 0.12 lb (AI)/acre/season.  Extremely Hazardous to Bees!
Lannate SP, LVR	4- 8 (SP) 12 - 24 (LV)	21 days to harvest grain or fodder.  3 days to forage.  Do not apply more than 2.25 lb ai/acre/crop.  Extremely Hazardous to Bees!
methyl parathion 4ER	8	12 days.  Do not apply during pollen shed. Extremely Hazardous to Bees!
Mustang MAXR,1	3.2 - 4.0	30 days grain or stover, 60 days forage.  Extremely Hazardous to Bees!
Penncap-MR	32 - 48	12 days.  Do not apply during pollen shed if bees are foraging in the area.  Extremely Hazardous to Bees!
permethrinR,1,2	See labels	30 days.  Liquids are Extremely Hazardous to Bees!
ProaxisR,1	2.56 - 3.84	21 days.  Apply as required by scouting or locally prescribed corn growth stages.  Do not apply more than 0.06 lb (AI)/acre/season.  Extremely Hazardous to Bees!
Radiant SC1	3 - 6	28 days. 3 days forage or fodder.  Highly toxic to bees!
Tracer1	1 - 3	28 days grain or fodder, 7 days forage.
RRestricted use pesticide.  1Labeled for chemigation.  2Generic active ingredient, may be additional formulations.

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.

 

Categories: Field corn, Insects, Armyworm

Date: 5/23/2008