gray leaf spot corn

 Pathogen

Cercospora zea-maydis Tehon & E. Y. Daniels. (Teleomorh: Mycospharella). Fungal structures: hyphae and conidia. It occurs throughout the Corn Belt from the mid-Atlantic to Nebraska and Colorado. Two populations characterized by the growth rate in laboratory media, geographic distribution, cercosporin toxin production, and molecular exploration have been described: one population occurs only in the eastern part of the Corn Belt and the mid-Atlantic. At the same time, the other is found throughout the USA. They are not different in susceptibility.

Symptoms of Disease

All corn hybrids and inbreds can Gray Leaf Spot (GLS). In plantations with a history of GLS, symptoms may appear on lower leaves before tasselling. Immature GLS lesions can be quickly confused with lesions involved by other pathogens; for example, eye pot (Kabatiella) and anthracnose (Colletrichum). Lesions that develop on leaves are rectangular and are blocked by leaf veins; taillights produce a yellow halo on most hybrids. Older lesions are detected and easily distinguished from other diseases. As the lesions spread, they merge and cause burns to large parts of the leaf. When the primary inoculum source is in the field, symptoms appear on the lower leaves and continue up the plant as infection occurs. When they are strong, the whole plant may be damaged. Cane infestations have been reported and can result in housing if severe. Lesions of sheath or husk tissue can be oval to ellipsoidal and are usually not diagnosed. Severely affected fields may appear to dry out quickly. The time from infection to the production of large inoculum is about 14-21 days for susceptible hybrids and 21-28 days for resistant hybrids.

Good Environmental Conditions

Temperature: 70°-90° F/25°-32° C, Relative Humidity: >12 hours @ > 90% RH, and Leaf Moisture: >12 hours of leaf wetness (from dew, rain, or irrigation).

Administration

Genetic Resistance

A tolerance/resistance Hybrid is the best choice for the GLS system. Resistant hybrids perform well under moderate to high disease pressure.

Cultural Practices

Tillage can reduce the risk of GLS as residues are incorporated into the soil and decompose. However, when other measures of the GLS system are used, such as crop rotation, resistant hybrids, and fungicides, the benefits of less tillage (e.g., increased water retention and reduced erosion) outweigh the negative effects of GLS.

Intercropping with crops other than maize for at least one year in low-risk fields (at least two years in high-risk fields) can reduce the severity of GLS.

Chemical / Pest Control

Under high disease pressure, using fungicides in time can significantly reduce the yield effect. These devices are expensive and usually only work when the disease pressure is high.