MEXICO CITY (AP) — U.S. Agriculture Secretary Sonny Perdue said Friday that he considers the United States' current farm-visa program to be "unworkable" but the issue probably will not come up in NAFTA talks that begin next month.

Many U.S. farms depend on temporary agricultural workers who enter on special visas, but there have been complaints about red tape, delays and limits on the program.

"Frankly we have a system now that's essentially unworkable for many farms," Purdue said during a visit to Mexico City, without elaborating.

While Mexico has said it wants an "integral" approach to renegotiating the 1994 North American Free Trade Agreement that addresses issues such as immigration, Perdue said the matter of guest workers was not likely to be involved.

Mexico has also suggested it could turn to South American grain if talks don't go well.

But Perdue displayed confidence in the competitiveness of U.S. grain, which supplies most Mexican feedlots.

"We have such productive and logistical advantages from the U.S. to Mexico, I think while they may talk about that, they may act as if they're having conversations, but we have a corner-store location for their supply," Purdue said.

Perdue noted that U.S. manufacturing has not benefited as much from NAFTA as the farm sector, and said President Donald Trump is "very rightly concerned about that." He also expressed hope that U.S. agricultural products will not be targeted in retaliation.

"The unfortunate thing is that in many trade renegotiations, or trade negotiations, the anxiety of our producers is that the agriculture is always used as a retaliatory measure," Perdue said, "and that's why I'm speaking to all of them, the president. .... Our goal is to do no harm in agricultural sector."