Fall Armyworms

When rain comes back to Central & East Texas, fall army worm infestations may develop (or already have) in pastures and hayfields. Larvae of fall armyworms are green, brown, or black with white to yellowish lines running from head to tail. A distinct white line between the eyes forms an inverted “Y” pattern on the face. Armyworms are very small at first, cause little plant damage and as a result often go unnoticed. Larvae feed for 2-3 weeks and full-grown larvae are about 1 to 1 ½ inches long.

Fall armyworm outbreaks in pastures and hay fields often occur following rainfall. Hay fields with a dense canopy and vigorous growth are often more susceptible to armyworm infestations than less fertilized fields. Irrigated fields are also susceptible to infestations, especially during drought conditions.
Look for fall armyworms feeding in the crop canopy during the late evening and early morning and during cool, cloudy weather. When fields are wet with dew, armyworms can stick on rubber boots while walking through the field.

The key to managing fall armyworms is frequent inspection of fields to detect infestations. During their final 2-3 days of feeding, armyworms consume 80% of their total diet. The density of armyworms sufficient to justify insecticide treatment depends on the stage of crop growth and value of the crop. Infestations of more than 2-3 armyworms (1/2 or longer) per square foot may justify an insecticide application. If the field is near harvest, an early harvest, rather than an insecticide treatment, is an option.