Cultural Practices of Limited Use in Soybean Rust Control

Soybean growers understand how cultural practices such as crop rotation can help with weed and insect control. Are there similar practices that can protect crops against soybean rust?

Growers in Brazil, where soybean rust has been entrenched since 2002, have had some success by planting early and growing short-season varieties. Although variety selection, planting date, fertility management, irrigation timing and other factors ultimately may prove beneficial, it is difficult to conduct research in these areas before the disease reaches the United States. Brazilian soybean growers also use early planted, early maturity varieties planted in small observation plots (<0.5 acres) used to provide early detection of soybean rust. These plots are scouted daily for disease symptoms and when discovered the entire soybean area is applied. Soybean rust symptoms can occur on nearly all stages of soybeans, but will "explode" in severity as the soybeans reach reproductive stage. The early planted and early maturity soybeans reach this stage first and indicate that the disease is present in the area and therefore fungicide treatments are required.

Compounding the problem, field conditions that favor soybean growth also are ideal for soybean rust:

• Temperatures between 59 and 83 degrees Fahrenheit
  
  
• At least six hours of moisture
  
  
• Additional moisture (rain or dew) to promote the spread after infection has taken place
  

It is unlikely that cultural practices alone will ever be able to protect plants against soybean rust, although they may be helpful when combined with disease-resistant varieties. Because resistant varieties will not be available for five to seven years, fungicide treatment remains the only viable option for protection.