Turcicum Leaf Blight
· Sorghum · Maize
The symptoms appear as small, oval, water-soaked spots on the lower leaves first. As the disease progresses, they start to appear on the upper part of the plant. Older spots slowly grow into tan, long cigar-shaped necrotic lesions with distinct dark specks and pale green, water-soaked borders. These lesions later coalesce and engulf a large part of the leaf blade and stalk, sometimes leading to death and lodging. If the infection spreads to the upper parts of the plant during the development of the cob. Severe yield losses can occur (up to 70%).
The fungus overwinters in the soil or on plant debris. Rainfall, night dew, high humidity and moderate temperatures favor the dispersion of the the fungus. Carried by wind or rain splashes it first spreads from the soil onto the lower leaves of young maize plants. Rainy conditions and poor field practices favor its spread to other plants and within fields. Optimal temperatures for infection are in the range of 18 to 27°C during the growing season. A prolonged period of 6 to 18 hours of leaf wetness are also necessary. Sorghum is another favorite host of the fungus.
Bio-fungicides based on Trichoderma harzianum, or Bacillus subtilis can be applied at different stages to decrease the risk of infection. Application of sulfur solutions is also effective.
An integrated approach with preventive measures together with careful cultural practices is recommended. An early preventative fungicide application can be an effective way of controlling the disease. Otherwise, fungicides can be applied when the symptoms are visible. Products containing carboxin, chlorothalonil or mancozeb can be applied. Seed treatments are not recommended.