South America Calling

Brazilian Soy Rust Threat

The arrival of Asian rust across Brazil's soybean belt from 2003 caused a certain amount of panic, prompting some to wildly speculate it may mean the end of the oilseed in the No. 2 soy-producing country.

Those predictions were wide of the mark, and subsequent years saw Brazilian farmers learn to control the Phakopsora pachyrhizi fungus through spraying pre-emptively and often.

However, experts warn that rust is acquiring resistance to the fungicides currently being employed, and there are no new products in the pipeline.

"We are seeing the existing products markedly losing efficiency," said Claudia Godoy, researcher at Embrapa Soja, a state crop research agency.

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There are three main groups of fungicides used to control rust -- triazoles, strobilurins and carboxamides. But the high number of applications over the last decade has fostered quickly resistant strains.

As many as five applications of fungicide is quite normal across the soybean belt, with reports of up to 10 applications not unheard of. Excessive spraying is one of the key issues concerning farm associations across the country.

"The tendency is for the situation to get worse," said Godoy.

Rust causes lesions on the leaves of soybean plants, which impede the formation of the bean and can result in massive yield losses. In more extreme cases, the fungus can kill the plant.

It spreads and intensifies throughout the season, reaching its nadir at around harvest time. As a result, more and more farmers plant short-cycle beans.

Across most of Brazil's main soybean regions, there is an enforced moratorium of soybean crops between June 15 and Sept. 15 in an effort to deprive the fungus of its habitat, but the tropical climate across Brazil's Cerrado allows some spores to survive a fallow period, especially where voluntary soybeans grow.

Eliminating voluntary plants and tight controls are vital to buy time to find new solutions to control rust, specialists say.

(AG)

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