Ug99, an aggressive race of the black stem rust fungus (Puccinia graminis) that has been spreading across Africa and the Middle East, has the potential to devastate wheat crops. Field trials conducted in Kenya by Bayer CropScience have successfully demonstrated that Ug99 can be effectively controlled by the cereal fungicide Folicur, the company said.

Folicur is already available to farmers in Kenya and Iran to combat stem rust. Bayer CropScience plans to register further fungicides based on Folicur in those two countries to control the disease.

That means growers in the United States also have the means to protect their fields, should the disease find its way across the ocean, says Randy Myers, fungicide portfolio manager for Bayer CropScience in the United States.

“There are a number of fungicides in our portfolio that are proven to control Ug99 in multi-year field trials,” says Myers. “Although it can be devastating to an untreated wheat field, U.S. wheat growers would be amply prepared for Ug99 with the fungicides available.”

Field trials conducted by Bayer CropScience have successfully demonstrated this unique race of rust can be effectively controlled by several of the company's established cereal-specific fungicides including Folicur, Stratego and the recently registered fungicide Prosaro.”

In 1999, African scientists made a discovery in Uganda that had serious consequences. Many wheat stocks were infested by a parasitic fungus that permanently weakened the plants, leading to a total loss of the harvest. The causative agent was a new, extremely aggressive variant of the black rust fungus (Puccinia graminis).

Scientists named this new race of stem rust “Ug99” after the country and year in which it was first observed. “It can be recognized from the dark orange to dark brown lateral pustules it forms on the stalks and leaf sheaths of the plants,” said Stefan Dutzmann, product development manager cereal fungicides at Bayer CropScience, describing the disease symptoms.

Since then, the pathogen has continued to spread. It has been reported in Kenya, Ethiopia, Yemen and Iran. No end to its proliferation is in sight. Fears that fungal spores may already have reached Pakistan have not been confirmed to date. From there, it is not far to the fields of India, the world's largest producer of wheat after Europe and China.

In the long-term, warmer regions such as Mexico and North America may also be at risk if fungal spores are introduced there, for example, by travelers.

The last large-scale outbreak of black stem rust in 1954 destroyed approximately 40 percent of the U.S. wheat harvest. It was not until many years later that resistant varieties of wheat were developed that cannot be harmed by black rust.