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Be aware of fall armyworms
Stacy Campbell
Stacy Campbell

Fall armyworm, Spodoptera frugiperda, can damage several important Kansas crops as well as pasture, turf, and home landscaping. This insect does not overwinter in Kansas. Rather, it is native to the tropical regions of the western hemisphere and is active year-round along the gulf coast and southern Florida, migrating in from these locations each year. Two full generations are possible in Kansas with defoliation and grain damage being the biggest concerns.

While reports of fall armyworm caterpillar damage have not been received so far this fall, it is a good idea to keep an eye out for this insect. Especially where newly seeded crops or grasses have been planted. 

Fall armyworm caterpillars can be distinguished from other Lepidopterans by markings on the head that resemble an inverted “Y” and four spots on the last abdominal segment that form a square. Once caterpillars are ½ to ¾ inch, they can do considerable damage in a few days. Because of this it is important to scout newly planted fields or hay meadows, in order to spot them when they are small. 

A reasonable treatment threshold is finding three or more caterpillars per square foot within a newly planted field. There are several insecticides labeled to control this insect including Mustang Maxx, Besiege and Sevin. For forage crops, be sure to check the grazing restriction and post-harvest interval. When considering a chemical treatment option, keep in mind caterpillars ¾-inch or longer are close to maturity and can be harder to control with an insecticide. 

Fall armyworm feeding declines with cooler temperatures and the adult moths eventually migrate south. In the meantime, be sure to keep an eye on any newly seeded grain or hay fields.  

K-State Research & Extension has crop insect pest management information available at your finger-tips, simply type into your internet browser “crop pest guides, KSU”. 

If you ever need any assistance in looking at your fields or have any questions, please give me a call at the Cottonwood Extension Office in Hays at 785-628-9430. 

Stacy Campbell is an agriculture and natural resources agent for Cottonwood Extension District. Email him at scampbel@ksu.eduor call the Hays office, 785-628-9430.