Understanding Soybean Rust and Its Effects on the Soybean Plant

Soybean rust is a very serious disease that results in substantial loss of soy crops around the world. Soybean rust had never been found in the United States, however, until November 2004, when it found in Louisiana. Most experts believe it reached Louisiana by spreading through winds, particularly hurricane winds. The ability for soybean rust to spread through wind by spores makes it an especially dangerous disease to the soybean plant supply around the world..

There are two different rust causing species of soybean rust disease that affect soybean plants. The most aggressive of the two is P. pachyrhizi. This species has long been found in Australia and Asia. It has also been more recently found on soybean plants in South America and Africa. This is also the same species of soybean rust that was identified in Louisiana in 2004. This species of soybean rust generally destroys 10 to 90% of soy crops.

Identifying Soybean Rust

It is important to catch soybean rust early, but this is not always an easy task. Soybean rust is often confused with other, less harmful, soybean diseases. The first symptom of soybean rust is yellow discoloration on maturing or flowering plants. This discoloration is located on the lower leaves.

When soybean rust advances, the infection spreads to both the middle and upper regions of the soybean plant. This causes the leaves to turn yellow. Lesions also appear and look like small brown pustules. When soybean rust reaches its advanced stage, the surface of the soybean plant has several reddish brown or tan lesions. Eventually, the soybean plant loses its leaves completely.

A soybean plant is more likely to be attacked by soybean rust if its leaves remain wet for extended periods of time. Soybean rust also favors plants grown in climates where the temperature stays between 50 to 80 degrees Fahrenheit. Since most soy crops are grown under these conditions, it is imperative to develop soybean plants that are rust resistant. Until then, early detection and application of fungicides is key in preventing soybean rust.

Fungicides

One fungicide used to control soybean rust Chlorothalonil, which is marketed under the names Bravo and Echo. Azoxystrobin, marketed as Quadris, and pyraclostrobin, marketed as Headline, are also fungicides used to control soybean rust. The use of these fungicides does substantially reduce the number of soybean plants affected by soybean rust. Unfortunately, the added costs of these fungicides also dramatically cut into the farmer’s profits.

Soybean rust is a serious threat to soybean farmers around the world. It is important to watch out for signs of soybean rust so they can be caught early in order to prevent the disease from further spreading.