Gray Leaf Spot
Gray leaf spot of corn is caused by the fungal pathogen Cercospora zea maydis.
The disease development depends on the varity of the maize hybrid and the weather conditions. That is the reason for a local severity infection in some places, where in others no infection was taken place.
Symptoms are seen on the leaves as small, point lesions surrounded by yellow halos. It is sometimes difficult to identify the disease at that stage. When lesions mature, they enlongate into narrow, rectangular, brown to gray spots and they expand parallel to leaf veins and become about 3,5 - 5cm long. Symptoms depend on the hybrid susceptibility and vary among them. Symptoms of gray leaf spots could be similar to other foliar fungal diseases such as anthracnose leaf blight, eyesport, or common rust. Symptoms of Gray leaf spot on maize Infection cycle of the fungal pathogen - The fungus survives during the winter on infected corn residues on the soil surface. With increasing temperatures in the spring spores are produced on maize residues and they splash to young leaves. Thats the reason why symptoms are commonly observed on the lower leaves of the plant. Spores are transported by wind or rain. - Infections occurr during long warm and humid conditions.
Temperature of 24°C to 30°C is optimal for the fungus as well as relative humidity of more than 90%. - Symptoms are seen after long periods of heavy dew, in areas where humitidy is very high and dew persist long in the morning. - C. zeae-maydis spores decrease development during periods with low humidity, but infection process starts again under high relative humidity. Each lesion can produce many spores, which are splashed by rain or transported by wind to young healthy leaves. There they survive until conditons are favorable for infection. - Due to the length of the infection process, symptoms may not be seen for some weeks after infection, depending on weather conditions and hybrid susceptibility. - Hot, dry weather will restrict disease development and distribution to other plants. - Gray leaf spot can have a great impact on the yield. The correlation of infected leaf tissue and the amount of yield is not clear. The lesions reduce the capacity of the plant of photosyntetic areas on leaves. Reduced photosynthesis could also lead to stalk rots and lodging. Conditions in Fieldclimate: - Hours between 22°C and 30°C/2,305*2 plus hours of rel. humidity (more or equal of 90%) during night/ 3,30*2 - range from 0 to 100%