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Corn+Soybean Digest

Vigilance A MUST For Rust

Brazilian Eloi Marchett, who farms more than 63,000 acres near Rondonopolis, Mato Grosso, is no stranger to Asian soybean rust and the devastation it can wreak.

Since rust was first discovered in South America (2001 in Paraguay), the extra fungicide costs Brazil farmers now pay to control it ranges from $750 million to $1 billion a year.

Like many farmers in Brazil, Marchett, who manages Carolina Farms, is savvy and refuses to be a casualty in the fight against rust.

“We start spraying for Asian rust at the R4 stage right through R6,” Marchett says. “Those who didn't spray lost 50-60% of their crop.”

Even at a cost of about $22/acre to spray, he believes it's simply the cost of growing crops in the soybean mecca of central Brazil. Carolina Farms uses four planes to aerially apply rust-fighting fungicides.

Nearly 60% of Mato Grosso do Sul, south of Mato Grosso, has soybean rust, says Geraldo Augusto de MeloFilho, a crop production specialist at Embrapa, a research entity similar to USDA. “Normally,” he reports, “farmers only spray after identifying, usually with one or two applications. We now have about 10 chemicals available for control.”

Physically getting fungicides to spray is often a major roadblock for controlling the fungus. Shipping across miles and miles of pot-holed and slippery muck roads makes disease fighting a struggle.

Within five years, however, MeloFilho expects resistant varieties to be available in Brazil.

In Africa, where soybean rust was first discovered in Zimbabwe in 2000 and South Africa in 2001, researchers are more optimistic about finding a resistant variety.

“We should have one in two to three years,” says Neal McLaren, plant pathologist at the Ag Research Council Grain Crops Institute in Potchefstroom, North West Province, South Africa. “But we don't know how long it (fungal resistance) will last.”

Spraying has been generally effective for controlling rust, McLaren says. “It's the odd person who is caught with his pants down and loses 60% of his crop.”

If farmers plant a longer growing maturity bean, they may need to spray two or three times, he says. If it's a shorter maturity, one spray may be enough. Spraying in South Africa runs about $9.60/acre; much cheaper than Brazil or estimates for the U.S. ($15-20/acre).

McLaren recommends their soybean farmers plant a one-acre indicator crop. “Farmers plant a shorter maturity variety early so if rust hits they have advance warning,” he says. “If you're in a borderline area, and not sure you'll be hit by rust, indicator crops are critical. In endemic areas where you know you'll have problems, spray.”

McLaren has also researched row widths to see if wider rows dry sooner and reduce the fungus' ability to spread. “Row widths of 18 in. and 36 in. didn't show enough difference to change planting width,” he says. “Rotating with corn doesn't help stop rust's progress either.”

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