Presence of Fall Armyworms Detected in Forage Sorghum in Western KY

The larval stage of the fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae) is a voracious defoliator of many plant species. The FAW is a native pest of the New World; however, it overwinters in south Florida or in the southernmost region of Texas (The Rio Grande Valley) in the continental USA. The adults are strong fliers and move northward during the summer months. In double-crop soybeans, fall armyworms can be devastating defoliators affecting plants from the seedling to V4 stages.

Impact in 2021

One common consideration in 2022 for entomologists and Extension specialists is to hypothesize about the presence of the fall armyworm for this growing season. In 2021, this pest caused an outbreak in many areas of the U.S.–from states around the Gulf of Mexico to Kentucky, many northern states, and Ontario and Quebec in Canada. In many areas, FAW caused devastating consequences for grasses, forages, and double crop soybeans. Dr. C. Teutsch (UK Forage Extension Specialist) found that in 2021 the economic impact of this pest to hay and pasture crops in Kentucky exceeded $5 million.

There are two strains of FAW, the rice and corn strains. In 2021, the rice strain (prefers to feed on rice, grasses, and forages) was the strain that caused the outbreak. In addition, for unknown reasons, this strain appeared earlier than in previous years; they were continuously migrating until late October and November. This strain might have been  resistant to pyrethroid insecticides.

Impact in 2022

In late June, 2022, FAW detection from Lubbock by a Texas A&M specialist found the highest FAW numbers in 12 years of trapping. Although this is alarming, this location is in the northwestern region of Texas and FAW migrant moths may take a different path. Furthermore, in contacts with Extension specialists from the southernmost area of Texas, the Rio Grande Valley, indicated by the end of July that FAW has not been a problem this year. This is an area where FAW overwinters or where moths migrate from Mexico to colonize the continental U.S.

This year, trapping of FAW in Lexington and Princeton in KY has not been high, and in most cases, captures have not been detected.  For example, last week, there were no FAW trappings in either location. However, be aware that a single FAW female can lay over 2000 eggs and populations can increase rapidly.

Here we are reporting the presence of FAW in a field of forage sorghum in Caldwell County. Larvae captured in this field were in different stages of development, from 1/3 inch to more than 1 inch in length feeding in the whorl (Figure 1). The percentage of damage observed along 5-foot samples ranged from 12% to 56%. Fall armyworm larvae were found feeding deep in the whorl, frass was visible from the outside (Figure 1), and characteristic feeding (irregular-shaped holes similar to grasshopper damage) was present on leaves (Figure 2).

Figure 1. FAW larva feeding on sorghum whorl (Photo: C.D. Teutsch, UK).

Figure 2. Characteristic FAW feeding on leaves, irregular-shaped holes ((Photo: Armando Falcon, UK).

The FAW appetite increases while larvae move from the first to sixth instar, and the defoliating damage is greatly noticed by farmers and scouting agents after the fourth instar. The six larval instar can be completed in 14 to 30 days, depending on the temperature.

Fall armyworm resembles corn earworm and armyworm; however, fall armyworm has a white inverted “Y” mark on the front of the dark head (Figure 2). Pupation occurs in the ground and adults can live up to 20 days.

Figure 3. A distinctive, light-colored inverted “Y” mark is present on the head capsule of fall armyworms. Also, pay attention to coloration changes of FAW larvae (Photo: Raul Villanueva, UK)

More Information

Watch for Fall Armyworm in Pastures (KPN 08/27/2019)

Fall armyworm in Featured Creatures (University of Florida) (Last updated 2019)

By Raul T. Villanueva, Entomology Extension Specialist, Armando Falcon-Brindis, Entomology Research Associate, and Christopher Teutsch, Forage Extension Specialist

Posted in Forages
%d bloggers like this: