Mature larvae are about 1.5 inches in length, smooth-bodied, and dark gray to greenish-black in color. 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 capsule is remarkable for its "honeycomb" 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 (inchworm) action. Larvae feed at night and on cloudy days, and hide under crop debris during sunny periods. One or more generation may occur per year.
Armyworm feeding is mostly limited to grasses, although this insect will feed on a number of other plants when starved. In Colorado, armyworm is mostly a pest of corn and spring grains, with only occasional infestations occurring in winter wheat. In Wyoming, grass hayfields are periodically damaged.
Armyworm outbreaks only occur occasionally because they have many natural enemies that usually prevent the development of economically significant infestations. Because of the sporadic and unpredictable nature of armyworm outbreaks, management options are limited to the use of insecticides. Scout for armyworm in field margins, low areas with rank growth, or areas of lodged plants. Look for feeding damage, frass (droppings) around the base of the plant, or plant material that has been severed by armyworm feeding and fallen to the ground. Check for larvae in and under debris around damaged plants and in heads of barley or wheat.
Consider treating armyworm infestations in small grains if all of the following conditions are met:
(1) Larval counts exceed the appropriate level in the following table (Table XII-4).
(2) Larvae are 0.75 to 1.25 inches in length.
(3) Most larvae are not parasitized. (Look for white eggs behind the head or small brown cocoons attached to the body.)
(4) Leaf feeding or head clipping is evident.
Table XII-4. Action thresholds for armyworm by damage: |
|
Situation |
Action Threshold |
Preheading- defoliation in lower leaves |
5 larvae per square foot |
Head clipping |
2 larvae per square foot |
Product List for Armyworm: |
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Pesticide |
Product per Acre (Fl oz. or oz. product) |
Preharvest Interval , remarks |
Baythroid XLR1 |
1.8 2.4 |
30 days to grain. 7 days graze. Do not apply more than 0.076 lb a.i. (4.8 oz) per season. W3 |
carbaryl1,2 |
See labels |
21 days to grain, 7 days to graze. W3 |
CobaltR1 |
13 – 25 |
28 days grain or straw. 14 days forage and hay. W3 |
lambda cyhalothrinR1,2 |
2.56 - 3.84 |
30 days to grain. Do not apply more than 0.48 pt per season. W,T3 |
Lannate LVR |
12 - 24 |
7 days. 10 days graze. W,B,O3 |
methyl parathion 4ER |
24 |
15 days. W,B,O,R3 |
Mustang MAX ECR1 |
1.76 - 4.0 |
14 days. W,T3 |
Penncap-MR |
32 - 48 |
15 days. W,B,O3 |
Proaxis R,1 |
2.56 - 3.84 |
30 days. Not more than 0.48 pt/A/season. . W,T3 |
Radiant SC1 |
3-6 |
21 days grain or straw. 3 days forage, fodder, hay. W,B,O,R,T3 |
Tracer 4E1 |
1 - 3 |
21 days grain or straw, 14 days graze. W,B,O,R,T3 |
RRestricted use pesticide. 1Labeled for chemigation. 2Generic active ingredient, other formulations available. 3Labeled on W (wheat), B (barley), O (oats), R (rye), T (triticale). |
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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. |
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Categories: Small grains, Insects, Armyworm
Date: 5/16/2008