Fall armyworm, Spodoptera frugiperda, is known to feed on over 80 host plants. In Kansas, it can damage several important 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.
In late June, large numbers of fall armyworm were being recovered from pheromone traps in the Texas panhandle. The offspring from these large flights have been emerging and are continuing to move north. Fall armyworm adults were detected in southwest Kansas pheromone traps during the first week of July and trap numbers are beginning to increase. Adult moths are most likely active throughout the southern portion of the state.
Start scouting now - at-risk crops should be scouted regularly for the remainder of the growing season. Caterpillars increase in size at an exponential rate and a majority of feeding occurs during the later stage of development. It is critical to scout thoroughly and treat, if needed, before the caterpillars are over ½ inch long. Larger caterpillars are harder to control and do the most damage. Recommended thresholds and products labeled for Sorghum Insect Management can be found at www.cottonwood.ksu.edu click onto the Crops and Livestock tab and look under Hot Topics.
Fall armyworm thresholds - Alfalfa: 1-2 caterpillars per square foot can destroy seedling alfalfa. 10-15 per square foot can destroy 12” tall plants. Corn: damage to whorl stage in early summer; treatment may be needed if 75% of plants are damaged. Bt corn may prevent ear damage. Sorghum: damage to whorl stage in early summer; treatment may be needed if 75% of plants are damaged. 1-2 larvae/head during flowering to soft dough reduces yield 5-10%. Wheat: Larval “window-paning” in early planted wheat can be a concern. If 25-30% of plants show damage, examine field frequently. Treat at 2-3 active larvae/ft.
Sorghum midge and sorghum aphid - have recently been found in Kansas, so growers are urged to be scouting their fields.
Historically in Kansas, the midge has been considered a minor pest confined to the southeast part of the state. Kansas producers have never actively treated fields for the pest.
“However, between 2017 and 2021, there were reports of large infestations resulting in significant losses in southwest and southeast Kansas,” reports Anthony Zukoff, Extension Entomologist, Garden City. “So far, there is no clear pattern to these events, and locations that experienced losses one year have not necessarily ended up with problems in the years following.”
Last week the first report of sorghum aphid (previously called the sugarcane aphid) was reported in Ellsworth County. “Every year since 2014 we have seen these aphids migrate into the state, generally being reported from south to north, and I would expect the same this year”, said Jeff Whitworth Extension Entomologist, Manhattan.
Since about 2018, however, they have not been as large or widespread a problem as they were in 2015-2017. Every year since 2018 sorghum colonies have been decimated by beneficial insects. “That is why you do not want to be too quick to make an insecticide application”, says Whitworth. Lastly when scouting fields keep mindful of one other insect pest—headworms. Once sorghum is between flowering and soft dough stages, headworms need to be monitored as well.
Stacy Campbell is an Agriculture and Natural Resources agent for Cottonwood Extension District. Email him at scampbel@ksu.edu or call the Hays office, 785-628-9430.
