Yellowstriped Armyworm on Tomatoes
At first glance, it resembled a mature fall armyworm caterpillar (Spodoptera frugiperda), being beige and about 1.5 inches long. As you can see in the picture below, the feeding damage on the leaves and fruit also mimicked fall armyworms. However, upon closer inspection, the markings on the caterpillar were not quite right. Mature fall armyworm caterpillars have white stripes along the lengths of their bodies, four dark spots on each abdominal section, and a white inverted
"Y" on their heads. On the other hand, the caterpillar we saw had two dark triangular markings on each abdominal section with a yellow or white strip below them and a faint inverted "V" on its head. We searched the internet and took our suspicions to Penn State entomologist Michael Skvarla, who confirmed it was a yellowstriped armyworm, a close relative of the fall armyworm.
You can find yellowstriped armyworms throughout most of the U.S., but they are more prevalent in the East. They feed on many crops, including beets, cabbage, carrots, cucumber, lettuce, potatoes, sweet potatoes, and numerous weeds. Occasionally, they reach numbers warranting management in our area. They can have multiple generations per year and various overlapping stages (egg, larvae, adult) throughout the growing season. However, none of the stages can withstand Pennsylvania winters. Cold weather limits their survival, which is a big reason yellowstriped armyworms are an occasional pest in the northeast and more of an issue in the southeastern states. In our case, we only saw a single worm the entire growing season.
Yellowstriped armyworms can move to vegetables from fresh-mowed alfalfa fields. Locating your vegetable fields away from alfalfa can help manage this pest. Digging a trench around your vegetable fields can also help but may not be necessary if you seldom see the caterpillars. Several parasitoid wasps and flies are natural enemies of yellowstriped armyworms. If yellowstriped armyworm populations are high, you can use the insecticides listed in the most recent edition of the Mid-Atlantic Commercial Vegetable Production guide. Insecticides for this pest are generally more effective when caterpillars are young or small.
