MONSTROUS FLOOD OF ARMYWORMS STRIPPING FARMPASTURES BARE

Writer: Robert Burns (903) 834-6191, rd-burns@tamu.edu
Contact: James Robinson (903) 834-6191, jv-robinson@tamu.edu

OVERTON — While the national media has concentrated on the widespread disastrous effects of Hurricane Georges, another disaster even more widespread in its range has besieged landowners throughout Texas and all across the South: armyworms.

“In my 20 plus years, they are the worst I’ve ever seen them,” says James Robinson, Texas Agricultural Extension Service entomologist based at Overton.

To make matters worse, chemical companies were caught unprepared for the severity of the infestation, and there may be a shortage of chemical control products.

The larval form of a migrating moth, the armyworm is named for its habit of moving across pastures in large numbers like the legions of an advancing army, devouring grasses in its wake. For farmers whose pastures and hay stocks have yet to fully recover from this year’s drought, the armyworm invasion must seem like literally the last straw. The worms are eating pastures right down to the ground, leaving neither leaf or stem for livestock, according to reports from county extension agents and farmers throughout East Texas.

Armyworm infestations have been regularly measured in East Texas fields in counts from 800,000 to more than 1 million worms per acre, or from 20 to 25 worms per square foot. To put this count in perspective, the economic threshold for treatment of armyworms, the level at which the farmer realizes more in returns from treating for the worms than he or she will pay for the chemical control, is usually considered three to four armyworms per square foot.

Extremely heavy infestations have been reported from South Texas to the Red River and from the grain growing regions of Central Texas to the Louisiana border. Counts are equally high from Arkansas to Florida and as far north as Oklahoma, according to Robinson.

A month ago, Robinson and other entomologists were warning of the possibility of heavy infestations of armyworms when rains returned. From years of observations, it’s known that armyworm populations often explode when rains follow an extended drought. But the severity of this year’s infestation caught Robinson and other entomologists by surprise.

Armyworm moths migrate in the millions northward from South Texas in the spring and summer. As part of their natural life cycle, each moth will deposit a clump of 50 or more eggs on individual blades of grass. During a drought, most of the eggs dry up or die within a few days. If the armyworms do hatch, they find nothing to eat and die.

The moths are persistent, however, and continue to migrate and lay eggs throughout the summer, drought or no drought. When their egg- laying coincides with a rainfall, the armyworms successfully hatch in droves and immediately start maneuvers.

Ten days after hatching, a mature armyworm measures 1 1/4-inches long. Its predominant color ranges from pale green to black, and it is marked by three parallel yellow lines running from head to tail.

Armyworm larva begin eating grasses as soon as they emerge. It is during the last three days before pupating that they become ravenous.

“During this stage they can strip a pasture bare almost overnight,” Robinson said.

In an average year, armyworms are relatively easy to kill. A treatment will typically cost $6 to $10 per acre depending on the product used and its rate of application. Some product labels stipulate that livestock must be kept from grazing the treated grass from a week to 14 days, further increasing the cost to the farmer. This year, several successive waves of moth generations have migrated up from the south. Though the farmer’s first treatment was successful, the next migration re-infests his fields. Many farmers have had to treat twice already. Most products are limited by law to two treatments in a season.

“It’s just as well that it’s not allowed. A third treatment would put their cost at $30 per acre. This late in the year, it’s unlikely that they would recover the cost of three treatments in terms of grazing or hay,” Robinson said.

Because of the severity of the infestation, and the shortage of chemical controls, farmers might be better off to wait until they plant winter pasture to treat for armyworms.

If farmers have grass remaining, haven’t treated twice and don’t plant to overseed small grain or ryegrass into their bermudagrass pastures, Dr. Gerald Evers, a forage management expert with the Texas Agricultural Experiment Station, Overton, recommended they treat a second time.

“If they lose all their grass, they’re going to have to sell their cows. That’s all there is to it. We’re already experiencing a hay shortage and it’s likely to get worse,” Evers said.

If, on the other hand, they do plan to overseed or if the grass is already gone, Evers recommended that they disk the summer grass stand. The disking will kill many of the armyworms and, to some degree, deny them further food supplies by turning some of the remaining plant material under. Evers also recommended waiting at least a week after disking to plant, giving the armyworms time to die off.

Robinson noted that more products are labeled for treatment of armyworms during establishment of winter pastures than for established pasture.

Robinson also noted that there is absolutely no risk to livestock or horses consuming armyworms during grazing or when fed armyworm-infested hay. It’s just extra protein for them, he said.

As bad as it seems for East Texas farmers, those in South Texas have it worse. Even a mild East Texas winter will kill off all the worms and farmers won’t have to deal with them until late next summer or early fall. In South Texas, the worms could continue cycling through generation after generation throughout the winter and into the spring, Robinson said.

For more information, producers should contact the county extension office.

Note to Editors: High resolution pictures of armyworms in the field may be found at http://overton.tamu.edu/bugs/

 

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