Louisiana wheat disease management
Leaf rust is usually evident later in the season than stripe rust. This is because the leaf rust pathogen requires warmer temperatures for development. Initial symptoms of leaf rust begin as light yellow spots, usually on the lower foliage. As the disease develops, small pin-point pustules form on the upper leaf surface. Pustules are brick or dark red and occur randomly on the leaf. Similar to stripe rust, pustules can cover the entire leaf surface if conditions remain favorable for development.
The disease develops optimally when nighttime temperatures are 50 to 70oF and leaves remain wet for 6 to 8 hours. Similar conditions favor the development of leaf and glume blotch diseases caused by Stagonospora and Septoria.
Effective disease management begins by selecting and planting high-yielding varieties with genetic resistance. Genetic resistance to wheat pathogens is extremely effective. In studies conducted by LSU AgCenter scientists over the past several years, fungicides were not beneficial when applied to resistant varieties. Therefore, planting resistant varieties can saved producers more than $20/A by eliminating the need for a fungicide application. Producers and consultants should check the disease package of their varieties before applying a fungicide. Data can be accessed here.
Genetic resistance is not bulletproof. This resistance can break down over time with pathogen populations evolving to overcome resistance. This was the case in 2010 when stripe rust was seen in AGS2060 (a stripe rust resistant variety).
Therefore, agents, producers, and consult-ants should always scout their crops beginning no later than early spring. In some cases, leaf and stripe rust can develop to very low levels in the fall. Detecting early infections will allow producers to plan for the spring.
When genetic resistance breaks down and disease is identified, a fungicide application may be needed. Typically, a single application at flag leaf emergence (F8) is adequate for managing most foliar diseases of wheat. Based on LSU AgCenter research, fungicides effective for man-aging leaf and stripe rust are Quilt, Stratego, Twinline or tank mixes of propiconazole (Bumper, Tilt, Propimax) and a strobilurin (Quadris or Headline). Propiconazole, tebuconazole (Folicur, Orius) or Prosaro are also efficacious against rust as well. Strobilurins may be applied alone; however, to optimize the effectiveness of these products, they must be applied before infection by the stripe rust pathogen.