Fall Armyworm, Spodoptera frugiperda, can damage several important Kansas crops as well as pasture, turf and home landscaping and is currently being reported across the state in various crops and pasture scenarios.  The first fall armyworm flight into Kansas occurred during the first week of July in south central parts of the state and trap counts of adult moths continued to increase in those areas through July while moths also started showing up in the central and northeast part of the state in notable numbers.  There were scattered and treatable infestations of caterpillars in these areas during that timeframe. During this first two weeks of August, fall armyworm moths are noticeable statewide. Trap counts of moths are increasing dramatically in south central areas and reports of significant infestations in the central and eastern parts of the state have been reported.

Given these recent trap observations and reports of caterpillar outbreaks, scouting should continue until the first frost of the season for at risk crops and pasture.  It is critical to scout often and treat, if needed, when the caterpillars are less than a half inch long.  Larger caterpillars are harder to control and do the most damage.  Recommended thresholds and products labeled for control of fall armyworm caterpillars (Table 1) can be found below.

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 is typically not a concern and will not impact yield.  Bt corn may prevent ear damage.

Sorghum:  damage to whorl stage in early summer is typically not a concern. 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. Very late second generation fall armyworm will be the biggest concern for wheat.  If 25-30% of plants show damage, examine field frequently.  Treat at 2-3 active larvae/ft.

Pasture/Brome: If damage is notable or there is window-paning, treatment may be warranted with 4 to 5 caterpillars per square foot.

You can read more about fall armyworm in turfgrass here.

Chemical Name	Trade Name	Mode of Action Class	Alfalfa	Corn	Sorghum	Wheat	Grass Forage/Hay
alpha-cypermethrin	Fastac CS	3A	yes	yes	yes	yes	yes
beta-cyfluthrin	Baythroid XL	3A	yes	yes	yes	yes	yes
bifenthrin	numerous products	3A		yes			yes
biological insecticide	Fawligen	–			yes
carbaryl	Sevin	1A	yes				yes
chlorantraniliprole	Vantacore	28		yes	yes	yes	yes
cyfluthrin	Tombstone	3A	yes	yes			yes
deltamethrin	Delta Gold	3A		yes	yes
gamma-cyhalothrin	Proaxis	3A	yes	yes	yes	yes
indoxacarb	Steward EC	22A		yes
lambda-cyhalothrin+chlorantraniliprole	Besiege	3A+28	yes	yes			yes
lambda-cyhalothrin	numerous products	3A	yes	yes	yes	yes	yes
methomyl	Lannate	1A	yes	yes	yes		yes*
methoxyfenozide	Intrepid 2F	18			yes
permethrin	numerous products	3A	yes
spinosad	Blackhawk	5		yes	yes	yes	yes
zeta-cypermethrin	Mustang MAXX	3A	yes	yes	yes	yes
zeta-cypermethrin+bifenthrin	Hero	3A		yes

Table 1. Registered products for the control of fall armyworm in Kansas crops.  For more specific information relative to any insecticide, always refer to the actual label on the product. *for use only in bermudagrass pasture

By Anthony Zukoff