What is it?
Corn armyworms are light tan to grey or dark brown caterpillars which attack many garden crops including corn, grasses and grains. Damage can be extensive and ruin a crop of corn if left untreated.
What does it look like?
Corn armyworms are usually between 1 1/2 and 2 inches in length and light tan to dark brown in color. Corn armyworms also tend to have either orange, yellow or dark brown contrasting stripes on their bodies. Damage on corn plants may first show up in the form of chewed or frayed looking leaves.
This damage usually occurs along the outside edges of the leaves, and eventually entire leaves may be eaten off. Additionally, as the feed through the leaves armyworms will bore into the corn ears themselves causing extensive damage as they feed until there is no more left to eat before moving on to another ear of corn.
How does it manifest?
The tan and grey adult females lay eggs among blades of grass or grains and from them caterpillars hatch. These caterpillars feed on nearby corn starting with leaves, stalks and then the actual ears of corn as they bore through. They will eat everything in an entire area and then move on to the next available food source.
Once the armyworms have fed for a period of several weeks, they then pupate in the soil and emerge once again as adult moths. This cycle continues until several generations of armyworms have been produced in a growing season. There will be more generations during times of cold, wet, spring weather because this is when they flourish.
What can you do about it?
If you notice damage on the leaves of your corn, or see actual caterpillars crawling on your plants you should either spray or dust the affected areas with diazinon containing insecticide. You may need to repeat the treatment every seven days until no further armyworms or plant damage is seen,
however the diazinon is slow acting on armyworms so it may take four or five days before you notice any improvement. Do not repeat applications any sooner than seven day intervals.