Sound the fall armyworm alarm

What comes to mind when you think about the fall of 2021? Is it the incredibly high fertilizer prices that more than doubled year-over-year? Or maybe it’s extremely sluggish supply chains for parts and machinery on the heels of COVID-19.

How about the historic invasion of fall armyworms?

According to entomologists, the fall armyworm outbreak of 2021 was the worst of its kind in nearly five decades. The insects infested pastures and hayfields in states from the mid-South to the northern U.S. border, chewing through grass and alfalfa stands that, in some cases, were stripped down to just stems.

Whisperings of another ambush are coming down the pipeline. One Alabama farmer told his local news station that fall armyworms have been wreaking havoc on alfalfa and bermudagrass since June. University of Georgia Extension agent Wade Hutcheson also reports pastures and hayfields in the Peach State are currently under attack with confirmed outbreaks in 90% of its counties. And an integrated pest management specialist with the University of Tennessee noted arrival dates for fall armyworm in his state are roughly two weeks ahead of schedule.

Entomologists and extension educators with The Ohio State University have also seen higher fall armyworm numbers than normal across 14 counties that are a part of their pest monitoring program. It’s too soon to declare an official outbreak in the Northern states, though, so rather than sounding a false alarm, these early observations should ring a bell about proactive pest management.

Blast from the past

Fall armyworm pressure was especially intense in 2021 because of three major factors: a warm winter, high tropical storm activity, and inefficient control practices. Although the triple-threat really rocked the hay and forage world for the first time three years ago, it was a recipe for disaster that entomologist Katelyn Kesheimer with Auburn University Extension predicted could become more frequent in future years.

Fall armyworms are migratory pests that overwinter in Florida, southern Texas, and parts of South America. Once the rest of the U.S. starts to warm up, the insects make their way to Northern states in the spring. However, an unusually warm winter in 2021 offered better insect survival, so a greater population of fall armyworms got a head start on migration.

This early venture north was not helped by the high winds from several hurricanes and tropical storms that pushed insects to a broader geographical range than what is typically seen. In fact, 20 more named storms occurred in 2021 than the yearly average, including seven more hurricanes. Two of the most notable, Claudette and Elsa, made long tracks through a wide swath of the eastern states.

Many regions have experienced similar conditions so far this year. For instance, much of the mid-South and Midwest welcomed abnormally warm weather and minimal snowfall last winter. According to the National Oceanic and Atmospheric Administration (NOAA), the hurricane season — which runs from June 1 through November 30 — also got off to an early start. And with peak hurricane season just around the corner, NOAA stated atmospheric conditions and warm sea surface temperatures support a 90% chance of above average storm activity through the rest of the year.

Winter weather and storm activity are completely out of our control, but producers can at least start scouting fall armyworm early and often. Time is of the essence when it comes to managing the destructive insects that move through pastures and hayfields with a vengeance. Seeing and spraying fall armyworms one day versus the next could be the difference between a high-quality late summer cutting and a field of alfalfa stems.

What to look for

It is easier to control fall armyworm when caterpillars are in younger instars. The specialists from Ohio note insect feeding accelerates rapidly as caterpillars grow, emphasizing the importance of early detection.

Fall armyworms can vary in color from green to tan to dark brown. They resemble many other caterpillar species, but an important identifier is the inverted Y-shaped stripe behind their heads. Scouting fall armyworm egg masses in and around pastures and hayfields can also inform the next steps of pest control.

“Look for egg masses glued not only to vegetation, but to structures like fence posts,” the specialists write. “Egg masses have a fluffy cover. When the cover is peeled back, eggs are pearly and tan when new, and they turn darker as they approach egg-hatch.”

Insecticides won’t penetrate egg masses well. With that said, pyrethroid-based insecticides are most effective when fall armyworms are less than 3/4-inch long, which leaves a short window to take action. Other products containing chlorantraniliprole may control larger caterpillars, but they will come at a higher cost.

The economic threshold for fall armyworm in forage is 2 to 3 insects per square foot. The specialists stress that small caterpillars have big potential for feeding damage and treating them with insecticide will most likely be cost-effective. An early hay harvest may also be a viable solution, but survivors could proliferate and affect neighboring stands.

“If survivors are abundant, an insecticide application may be warranted to protect nearby fields,” the specialists state. “Armyworms get their name from moving in large bodies, or marching, to new feeding areas.”

Fall armyworms are currently in their second generation. Given the jumpstart to pest life cycles granted by a warm winter, a third generation can be expected, and the two generations could overlap. Continue to diligently scout through the fall since pest populations can exhibit exponential growth. If fall armyworm damage does occur in alfalfa or grass stands, harvest forage to salvage what is left, and then let the field rest.

“Established alfalfa should come back from fall armyworm damage,” the specialists affirm. “Recovery of a cool-season perennial grass will depend on the relative severity of the damage, the overall health of the stand going into the infestation, and how many young tillers were not consumed. It is hard to predict how they will recover,” they add.

The presence of fall armyworm in the South should alert farmers farther north to be on the lookout. Considering the devastating effect the pest had on production the last time it trooped through pastures and hayfields, it is worth being on watch for another outbreak. Whether fall armyworm strikes this fall or not, keeping these scouting tactics in mind will be critical in the years to come.