Soybean Rust: A Persistent Invasive Threat to Soybean Production

Soybean rust is one of the most significant invasive diseases affecting soybean production worldwide. Caused by fungal pathogens in the genus Phakopsora, the disease can spread rapidly under favorable environmental conditions, leading to premature defoliation, reduced yields, and increased production costs for farmers.

Since its arrival in the continental United States in 2004, soybean rust has remained an important concern for agricultural producers, researchers, and plant health agencies. Ongoing monitoring, forecasting, and early management are critical to limiting its impacts and protecting one of North America’s most valuable crops.

What Is Soybean Rust?

Soybean rust is caused by two closely related fungal pathogens:

• Phakopsora pachyrhizi – the more aggressive and economically important species
• Phakopsora meibomiae – a less damaging species that has not been detected in the continental United States

Of the two, P. pachyrhizi is responsible for nearly all major soybean rust outbreaks worldwide. The disease infects soybean leaves, where it produces small lesions and raised pustules that release large numbers of microscopic spores. These spores can spread quickly across fields and regions when environmental conditions are favorable.

Soybean rust is capable of infecting soybeans at any stage of growth, but infections that occur during reproductive stages often result in the greatest yield losses.