The USDA said June 30 it will collaborate with Mexico to watch and eradicate New World screwworms, a pest for cattle. (Photo courtesy of USDA-APHIS)

The USDA will gradually reopen the southern border to imported cattle, bison and horses, saying it and Mexican counterparts have agreed to step up a campaign to detect and eradicate New World screwworms.

The department will reopen the Douglas, Arizona, point of entry on July 7 and tentatively plans to reopen four other border crossings in New Mexico and Texas by mid-September.

Agriculture Secretary Brooke Rollins closed the border May 11 in response to screwworms being detected in Mexico about 700 miles south of the U.S. No northward movement of the flesh-eating maggots has been detected in the past eight weeks, according to the USDA.

“We are continuing our posture of increased vigilance and will not rest until we are sure this devastating pest will not harm American ranchers,” Rollins said in a statement.

About 60% of the cattle imported into the U.S. enter from Mexico. The National Cattlemen’s Beef Association CEO Colin Woodall said reopening the border was a “measured, thoughtful approach” to allow some trade while protecting the cattle industry.

The border should remain closed until screwworms are eradicated from Mexico, said R-CALF, a cattlemen’s group that argues beef imports are hurting U.S. producers.

The closed border and high cattle prices are giving U.S. ranchers an incentive to enlarge herds, R-CALF CEO Bill Bullard said. “We see no particular reason to increase the risk to our herds at this time,” he said.

“This is a devastating pest. We don’t understand why USDA would expose our cattle industry to this risk,” Bullard said.

New World screwworms were eradicated in the U.S. and Mexico by the 1980s, but are endemic in parts of South America and the Caribbean. Screwworms in 2022 breached the Darien Gap, a jungle between Colombia and Panama, and reached southern Mexico last November.

Mexico will renovate a laboratory in southern Mexico to increase the production of sterile male New World screwworms flies to 60 million to 100 million a week, according to the USDA.

The USDA releases the sterile flies from the air, frustrating reproduction efforts. The USDA said it hopes to eventually produce 400 million to 500 million sterile flies a week to push screwworms back across the Darien Gap.

Mexico also has agreed to let the USDA airdrop sterile flies seven days a week. The Mexican government had restricted flights to six days a week.

After opening the border in Arizona, USDA tentatively plans to reopen the border July 14 at Columbus, New Mexico; July 21 at Santa Teresa, New Mexico; Aug. 18 at Del Rio, Texas; and Sept. 15 at Laredo, Texas.