When Armyworms Attack: Evaluating Brome Fields After a Tough Year
By Lonnie Mengarelli, Extension Agent – Crops and Natural Resources

This past year proved challenging once again for forage producers across eastern Kansas. In 2025, fall armyworms arrived in late July and overstayed their welcome through a long, warm fall. Many producers reported partial or complete loss of smooth brome stands, leaving fields that range from lightly affected to areas that appear completely dead.

The level of damage varied widely from field to field. In many cases, the hardest-hit areas were fields that had been harvested in mid-to-late July. Those freshly cut fields created the perfect environment for fall armyworm moths to lay their eggs. Armyworm moths are not particularly picky — they will lay eggs on nearly any foliar material available. Once the larvae hatch, they begin feeding and can quickly move in large numbers across a field in search of food.

Smooth brome is a cool-season grass, which means it does not perform well during hot summer conditions. When a field is cut in late July, the plant is already growing under stress from high temperatures that often reach into the 90s. After cutting, very little leaf material remains, leaving the crown only a few inches tall and exposed. When armyworm feeding occurs under those conditions—especially if rainfall is limited—the result can be rapid browning of the field.

Some fields showed signs of recovery after late-season rains, but others never fully greened back up. With the warmer temperatures we’ve experienced moving into this spring, many producers are asking the same questions: Are the brome plants still alive? Is there potential for regrowth?

Unfortunately, a quick drive-by assessment may not provide an accurate answer. Dormant perennial grasses can sometimes look similar to annual weeds that died over winter. The only reliable way to know is to examine the plants directly.

One method is to check for living rhizomes. Dig up a clod of grass and examine the underground stems. If the rhizomes are alive, new tillers should begin emerging as temperatures warm and precipitation returns. Signs of life include firm roots holding soil and green tissue beginning to develop near the crown.

Another useful method is what many call a “bag test.” Collect several plant samples from the field and rinse the soil from the roots. Trim the shoots to about an inch above the crown and remove most of the roots. Lightly moisten the crowns with tap water and place the samples in a sealed plastic bag. Leave the bag at room temperature, out of direct sunlight, for two to five days. Living plants will typically begin producing small shoots or roots. If there is no growth after about six days, the plant is likely dead.

If stands are severely damaged, producers will have several management options to consider.

In a typical year with stable input costs, the recommendation might be to prepare a seedbed and reseed brome at 10 to 15 pounds of pure live seed per acre. Poor seedbed conditions may require seeding rates closer to 20 pounds per acre. As always, soil sampling should guide fertility programs so that lime and nutrients such as nitrogen, phosphorus, and potassium are applied appropriately.

However, with rising costs for seed, fertilizer, and other inputs, spring reseeding may not always be the most economical option. Spring plantings also tend to face heavier weed pressure and typically cannot be harvested until the following year.

Some producers may instead consider alternative forage crops to help fill the gap. Summer annual forages such as pearl millet, sorghum-sudangrass, forage sorghum, or crabgrass can produce between 4,000 and 8,000 pounds of forage per acre under good conditions. Cool-season options like spring oats, triticale, or cereal rye may provide 1,500 to 4,000 pounds of forage and can be useful for early-season grazing or hay production.

Another option is patience. If immediate forage production is not essential, waiting a few weeks to monitor stand recovery may help producers make a more informed decision. This approach allows time to evaluate plant health, watch input costs, and observe market conditions. Of course, there is always some risk if the stand fails to recover and forage yields fall short.

For producers who depend heavily on brome hay sales and have fields that clearly did not survive the winter, reseeding may ultimately be the best path forward. When reseeding is necessary, determining the exact acreage affected and planning for seed, fertilizer, herbicide, and potential insect management will help reduce surprises later.

The important thing to remember is that every field will be different. A neighbor’s plan may not be the right solution for your operation. Taking time to evaluate each field, inspect the plants, and weigh the available options will help determine the best path forward for your forage system.

After a year like 2025, one thing is certain: careful field evaluation this spring will be the key to making sound management decisions for the season ahead

Lonnie Mengarelli is a K-State Research and Extension Agriculture agent assigned to Southwind District. He may be reached at [email protected] or 620-223-3720