Red imported fire ants are marching toward the Pacific Northwest. Actually, it's more like they're hitching rides — hay rides, that is.

“I think hay is one of the No. 1 ways the fire ant spreads because hay shipment is unregulated,” says Charles Barr, Texas A&M University entomologist.

Red imported fire ants currently infest more than 320 million acres in 12 Southern and Eastern states and Puerto Rico, according to USDA-ARS. They have spread to California and New Mexico in recent years.

The pests have cost the Texas cattle industry alone $67 million, according to a survey Barr has conducted. That's a “fairly conservative” figure compared to what other studies have shown, he adds. The ants kill newborn calves, damage haying equipment and ruin feed.

“Most of our good hay-producing counties are infested,” adds Chris Sansone, another Texas A&M entomologist.

Some scientists believe the Pacific Northwest's mild, wet winters will make that region an ideal home for fire ants, at least west of the Cascade Mountains.

“If it goes up the state into Oregon, people have to worry,” says Gary Hayakawa, who owns Three Star Nursery in Orange County, CA. After red imported fire ants were found in hay in Orange and Los Angeles counties in 1998, USDA declared a quarantine. Hayakawa and other nursery owners now must bait, inspect and treat for the pest.

Fire ants build mounds up to 1.5' high and 2' across. The mounds are so numerous they sometimes damage pasture land and haying equipment, force operators to leave hay standing, or cause people to shift from sickle mowers to disk mowers.

A 1999 Texas A&M study compared total costs per acre of haying with a 100-hp tractor and sickle mower in infested and non-infested hay fields. It showed that the ants increased costs by $5.40/acre. The hay field in the study had about 40 fire ant mounds/acre, Sansone notes.

Hay producers tell Barr they have to drop down a gear in mound-infested fields. That's a 20% loss of time, extending a 10-hour day to 12 hours, Barr notes.

Fire ants like low, wet areas, Sansone says. He recommends that growers remove bales from fields quickly, especially if it looks like rain.

The ants can infest hay bales quickly. In a Texas study, 60% of square bales tested became infested in three days; 100% were infested in a week, Barr says.

Sansone advises growers to treat areas where hay will be stored. Placing pallets on the ground and stacking bales on top can help, too.

“It gets the bales off the ground,” Sansone points out.

The pallets won't completely stop the ants; they could build mounds under the stacks. But if the fire ants move in, baits can be placed under the bales.

To control fire ants, growers can apply Amdro Pro or Extinguish insecticide bait, or a combination of the two. They're the only baits labeled for use in hay that will be fed to food animals, Barr says.

“Regular Amdro is not pasture-labeled,” he adds.

Some biological control agents are also being researched. Barr recently used Brazilian phorid flies with baits and another naturally occurring parasite called Thelohania solenapsae to keep fire ants manageable on 300 acres at a working Texas ranch.

The flies are natural enemies of the ants and are not known to attack anything else, Barr adds.

Before treating hay land for fire ants, growers should consider the amount of time and hay lost, Sansone recommends. “If you are losing more than $15/acre, then you can justify that application.”

Growers with 20 mounds an acre or more can at least break even

At losses of $7-8/acre, “you can justify some treatment using broadcast baits,” Sansone says. “You can at least make that investment back.”

People who can't afford the $10-12/acre baits can lightly disk or drag fields to knock down mounds, Barr says.

For more on fire ants, visit: fireant.tamu.edu or www.cdfa.ca.gov/phpps/pdep/rifa/index.htm.