Fall Armyworms Marching Our Way

With the upcoming rain in the forecast, be on the lookout for armyworms. In case you are unaware of what I am talking about, they are invasive little worms eating up yards, pastures, crops and everything in their paths. There are multiple species of armyworms present in Texas:  the fall armyworm, the yellow striped armyworm, the true armyworm (common during April and May), etc. But right now we are being invaded by the fall armyworm. The fall armyworm is most abundant during August through early November and feeds primarily on Bermuda grass, wheat and rye grass, but it is not picky. It will eat almost anything green in sight when their primary food sources are scarce.

Fall armyworms are green, brown and/or black. They have a distinct white line between their eyes that forms an inverted “Y” pattern on their face. When feeding during this stage, the larvae strip foliage and then move to the next available food. High populations appear to march side by side as they move to new food sources, which is how they got their name armyworm.

The pupa stage follows the caterpillar stage. Full grown armyworms tunnel into the soil and transform to the pupae, an inactive non-feeding stage. In a 7-10 day period, a moth will emerge from the pupa and repeat the life cycle. This moth is distinctive in that the front pair of wings is dark gray with an irregular pattern of light and dark areas. These moths are nocturnal and commonly found around lights. A single female moth can deposit up to 2000 eggs in her lifetime. This entire life cycle is less than one month long, so it does not take much time for armyworms to cause massive destruction!

Development will end with the cold weather in November, but that gives little hope right now as they are destroying your property. The key to managing fall armyworms is to detect infestations before they have caused economic damage. Larvae feed primarily during the night and during cloudy weather. Once larvae are greater than ¾ inch, the quantity of leaves they eat increases dramatically. During the final 2-3 days of feeding, armyworms consume 80% of the total foliage consumed during their entire development. This is how extensive damage can be done in a couple of days.

There are a couple of natural enemies – parasitic wasps and flies, ground beetles, and insect viruses help suppress armyworm numbers. However, these natural enemies can be overwhelmed when large numbers of migrating moths move into an area and weather conditions favor high survival of eggs and larvae. Like most things, there is a tipping point where these predators cannot keep up; they can become overwhelmed when large numbers of migrating moths lay thousands of eggs in a field. If natural enemies are not enough to help, there are a number of insecticides labeled for armyworm control in pastures and hay fields. Some insecticides have grazing and/or haying restrictions so please read and follow all label recommendations.

For more information on insecticides for armyworms or more information, please contact Chelsea Dorward at the Texas AgriLife Extension Service – Bosque County Office at 254-435-2331

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