9/10/2020

Field Facts: Southern Rust in Corn

Southern rust in corn (also known as Polysora rust) is a potentially devastating crop disease that has begun spreading further intothe Corn Belt from its traditional home in tropical and subtropical areas. It poses a greater threat than common rust due to its ability to rapidly develop and spread under favorable conditions.

Symptoms
Orange or reddish-orange pustules form on the upper surface of corn leaves. Unlike the elongated, jagged shape of common rust, southern rust pustules are typically circular.

Geography
Southern rust is more prevalent in tropical and subtropical regions, including the southern United States. While not traditionally common in the Corn Belt, southern rust has begun to appear further north earlier in the season, particularly when temperatures are higher than average. The disease has been detected in Illinois, Indiana, Iowa, Nebraska, Kansas, South Dakota and Wisconsin in recent years.

Timing
This disease typically appears later in the growing season.

Conditions for Development
High humidity and high temperatures create the perfect conditions for southern rust to develop rapidly. Spores are spread by wind and rain from Mexico and the Caribbean, where the disease overwinters.

Scouting Tips
Begin scouting 2 weeks before tasseling and watch for southern rust until 2 weeks after tasseling. Check for disease in both the lower and upper levels of corn when scouting for southern rust.

Effect on Yield
Southern rust can cause substantial yield losses if disease pressure is severe. Significant damage to upper leaves early in the life of a hybrid increases potential yield loss. Often the latest-planted corn is at a higher risk for yield loss.

Management Tips
Aproach® Prima fungicide from Corteva Agriscience has two modes of action that provide excellent control of southern rust. Fungicides applied preventatively, just after initial disease detection, with the correct water volume for maximum canopy coverage may provide a profitable return.

When determining if application is warranted, factors to consider include:

  • The crop stage
  • The severity of the infection at the time of application
  • The weather forecast being conducive to disease development
  • The probability of other fungal leaf blights developing in the field
  • The price of corn
  • The cost per application.

Fungicide treatments are more likely to be profitable during severe rust outbreaks while corn prices are high and with disease presence on younger stage corn.

Aproach® Prima is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.