The Hayfield Picked Up a Second Pest, and It Arrives After the Rain

The advisory landed Tuesday morning, and by Tuesday evening AgriLife Extension had published its own accounting of what this fall has already done to Texas hay. Neither outfit coordinated with the other. Both are describing the same field.

Texas Farm Bureau urged ranchers this week to walk their pastures and hay meadows looking for fall armyworms, saying cooler temperatures and rain events across the state in early October created the conditions the insect needs.

"Ranchers should check their pastures and hayfields regularly, especially after rainfall," Tracy Tomascik, the bureau's associate director of Commodity and Regulatory Activities, said in the notice. "Catching an infestation early can help ranchers determine the best course of action."

The timing matters because of how the insect behaves. Fall armyworm larvae feed hardest in the late evening and early morning and during cool, cloudy stretches, and they hide low in the plant canopy — beneath fallen leaves or right at the soil surface — when the day turns hot. A scout walking a field at two in the afternoon on a bright day is looking at the wrong hours in the wrong layer of grass.

That is the trap Tomascik pointed at. Larvae are small at hatch and easy to miss, then eat progressively more as they mature, so the damage curve is not linear. Fields that looked fine last week can be ragged this week. The recommendation is frequency, not a single inspection: walk through, part the grass, check the vegetation around the stand rather than only the stand itself.

The threshold the bureau cited is concrete. In some situations, more than two to three armyworms per square foot — each at least half an inch long — may justify an insecticide application. If hay is close to harvest, cutting early can substitute for a spray. Any product used has to follow its label.

Identification is worth carrying into the field, because several caterpillars turn up in Bermuda grass this time of year. Fall armyworm larvae range from green to brown to black, carry light-colored stripes down the body, and have a white, inverted Y-shaped marking on the front of the head. AgriLife Extension keeps a dedicated fact sheet on control in pastures for the management detail.

What makes this advisory land harder than the same notice in an average October is the state of the forage. AgriLife Extension reported this week that Coastal Bermuda growers in parts of Texas are taking three or four cuttings where they used to take seven or eight, with the pasture mealybug stacking on top of drought — a pest that injects a toxin, reddens the grass and has been spreading north toward the Oklahoma line since it was first noticed in the state in 2022. Hay has also gotten more expensive to put up, between diesel and net wrap, which raises the cost of every ton the armyworms take.

An armyworm infestation does not have to be statewide to hurt. It has to hit the field that was already going to be short.

There is one structural reason the pest keeps surprising people. Fall armyworm is a migrant, not a resident: moths overwinter in South Texas, southern Florida and Mexico and ride weather systems north through the season, laying successive generations on whatever forage is available. An infestation can appear in a field that showed nothing a week earlier, which is why the bureau's advice leans on repeated scouting rather than a calendar date.

For ranchers who find larvae at threshold, the sequence is unglamorous — confirm the species, count per square foot, weigh the spray against the value of the cutting, and read the label. For everyone else, the work this week is a walk through the grass with the grass parted, before the bare patches do the counting for them.

Ranchers who took three cuttings instead of eight this year can find the economics behind that number in our report on the pasture mealybug's hay toll.