Asian Soybean Rust

Asian Soybean Rust

Asian Soybean Rust

Asian soybean rust (Phakopsora pachyrhizi) is a fungal disease that can quickly defoliate plants and reduce pod set, pod fill, seed quality and yield. The disease is found in every soybean region in the world. It was recently confirmed in the southern United States and is expected to spread to other parts of North America during the upcoming growing season. All soybean-growing areas of the United States are at risk. However, based on 30-year averages, the most favorable weather conditions for the disease occur in the Mississippi delta region and the Ohio and Mississippi river basins in the Midwest.

Who is at risk?

In general, southern growing areas are at greater risk than northern areas, because of the longer growing season; the warm, humid climate is favorable for rust development; the presence of alternative hosts such as kudzu; and proximity to overwintering areas. Risk analyses indicate that Phakospora pachyrhizi could cause yield losses of greater than 10% in any U.S. soybean-growing region, whereas in southeastern coastal states losses up to 50% are possible. Actual losses will depend on weather conditions during the growing season and where and when the pathogen enters the country.


The most common symptom of infection by P. pachyrhizi is tan-to-dark brown or reddish brown lesions (spots) which are usually clustered alongside the veins. The disease begins with small, water-soaked lesions, which gradually increase in size, turning from gray to tan or brown. They assume a polygonal shape restricted by leaf veins and usually coalesce to form larger lesions. As the plant matures and sets pods, the symptoms spread rapidly to the middle and upper parts of the plant. Lesions are found on petioles, pods, and stems but are most abundant on leaves. Especially at the early stages, it is easy to confuse the symptoms of soybean rust with symptoms of three other soybean leaf diseases : brown spot, caused by the fungus Septoria glycines; bacterial pustule, caused by Xanthomonas axonopodis pv. glycines; and bacterial blight (also called angular leaf spot), caused by Pseudomonas savastanoi pv. glycinea.

Can Asian Soybean Rust's spread be halted?

No. As more land was planted into soybean around the world, the spread of the pathogen causing Asian soybean rust eventually would follow.