Soybean rust, Phakopsora pachyrhizi, was first detected in the U.S. in 2004 in Louisiana. It is a more aggressive species of soybean rust (SBR) than P. meibomiae. P. pachyrhizi has been known to infect more than 90 species of legumes; some of these may serve as reservoirs. As its name implies, one of its most economically important hosts is soybean.
Environmental conditions affect the incidence and severity of the disease. Temperatures between 59 and 86oF and humidity of 75 to 80% is required for spore germination. Spores can spread with wind or on clothing of individuals walking through infested fields. Signs of soybean rust begin on lower leaves as small lesions that increase in size on the undersides of leaves. Infection spreads to middle and upper leaves shortly after pod set.
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