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Corn+Soybean Digest

Surprise ASR Hits Portions Of Mexico

A bout of Asian soybean rust left more than 20 soybean seed growers near Tampico, Mexico unexpectedly dealing with the disease. About 320 hectares, or 650 acres, were affected, resulting in defoliation and potential large yield losses.

ASR infections began in January but became increasingly noticeable in March and April. “It caught these particular growers by surprise, and it hit them pretty hard,” says Dr. Marty Wiglesworth, Syngenta technical brand manager, fungicides.

Seed beans are generally harvested at the end of April into early May, so the majority of the affected acres should be out of the ground. Mexican growers will begin planting more soybeans closer to the Texas border in late May. According to Wiglesworth, the time gap between harvesting the seed beans and planting additional soybeans may be good news for U.S. soybean growers.

“We cannot foresee whether the impact on the U.S. crop will be minimal. We don’t know at this point,” Wiglesworth says. “It depends on whether there are nearby patches of volunteer soybeans or kudzu for ASR to live on until the newly planted Mexican crop becomes susceptible at R1. Scouting fields is the prudent thing to do, and the universities and Syngenta are actively engaged in scouting activities.”

Potentially, Wiglesworth said ASR could be equated to the wheat rust that comes yearly out of Mexico and Texas into the Midwest. “If ASR establishes itself on a regular basis in Mexico, one possibility is that it could follow a very similar pathway as wheat rust. Overwintering ASR present in Florida and Georgia has a harder time moving directly into the Midwest unless there are unusual weather patterns, but Mexico could serve as a more consistent source into the Midwest. At this time, however, experts believe the current risk for rust in east Texas is low.”

There are currently no effective fungicides labeled for use in Mexico for Asian soybean rust control, although agrichemical companies, including Syngenta, are currently pursuing emergency exemptions for rust specific fungicides.

More information about soybean rust is available at or at

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