How to Control Armyworms

Two Methods:Control Armyworms in GrassControl Armyworms in the Field

Armyworms are green-striped caterpillar larvae of the adult armyworm moth. Armyworms got their name because they travel in small armies, eating everything in their path. A common pest of grass, armyworms will also eat corn, beets, beans, clover, flax, millet and other grains.

Method 1
Control Armyworms in Grass

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    Look for early signs of armyworm damage. Because they feed at night, you may not see the caterpillars right away. The earlier you treat the problem, the easier it is to control and less damage a lawn will sustain.
    • An increase of the number of birds in your yard may be an indication of armyworms. Birds eat the caterpillars, but usually do not eat enough of them to keep the infestation under control.
    • Brown spots on your lawn are often the first sign that you have an armyworm problem.
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    Mow the grass short and then water it well to move the caterpillars out of the thatch.
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    Spray the grass heavily with a liquid insecticide following manufacturer directions. Granular insecticides are generally less effective against armyworms than the liquid ones.
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    Leave the sprayed lawn alone for at least 3 days without mowing or watering to give the insecticide time to work.

Method 2
Control Armyworms in the Field

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    Monitor your fields in spring for signs of armyworm damage. Look for holes in the leaves or pieces missing off of leaf edges where the armyworms have eaten them.
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    Look under the plants for armyworms or signs of their frass, or droppings. You may also find larvae under plant debris lying in the field. If you are growing barley or wheat, you may find worms inside of the heads.
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    Mow the field if armyworms have infested your hay fields. As the hay dries, the armyworms loose interest in it as a food source and move on.
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    Apply insecticides to the field using ground or aerial equipment The following insecticides are proven effective on controlling armyworms:
    • Asana XL should be used only on corn crops and should not be applied within 21 days of harvest.
    • Permethrin is also only for use on corn and should not be used within 30 days of harvest.
    • Carbaryl (Sevin) may be applied either to corn or wheat. Do not use more than 2 applications and do not it apply within 21 days of harvest.
    • Ethyl is useful for corn, sorghum and all small grains but can only be applied with an aerial application. Do not apply ethyl within 12 days of harvesting corn or sorghum, and within 15 days of harvesting small grains. After you apply the ethyl, post notice that the field is being treated and stay out of it for 3 days.
    • Lorsban can be applied to corn and sorghum. Do not allow livestock to graze in a field for at least 15 days after you apply lorsban. Do not feed meat or dairy grains treated with Lorsban until at least 35 days have passed.
    • Lannate or Malathion can be used on all crops. Do not spray these insecticides within 7 days of harvest and stay out of the field for 2 days after treatment.
    • Methyl is used for aerial application on corn and small grains only. Do not apply it within 12 days of a corn harvest, or 15 days of a small grain harvest. Post notice in the fields and stay out of them for 2 days.
    • Warrior can be used in corn, sorghum or wheat fields. Do not apply it within 20 days of corn harvest or 30 days of sorghum or wheat harvest.


  • There are typically 2 to 3 generations of armyworms each year. The first generation usually does the most crop damage because weather conditions are right for them and plants are smaller and more vulnerable to their attack.


  • If the armyworms are larger than 1-inch (2.54 cm) long, the damage to your crop may already be too extensive for control to be cost effective.

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Categories: Garden Pests and Weeds | Pest Control