Initial symptoms appear as small, pale green to yellow chlorotic spots scattered over the leaf blade. These spots later enlarge and develop into circular or oblong lesions (3 to 20 mm) with bleached and dried centers and dark brown irregular margins. In severe cases, they coalesce and blight the entire leaf. Minute black specks are visible within the lesions on the underside of leaves. If the infection occurs during the early stage of plant growth and the upper leaves are blighted before flowering it can lead to severe yield losses.
The disease is caused by the fungus Phaeosphaeria maydis, which overwinters in crop debris. During favorable conditions, its spores are propagated to new plants by rain splashes and wind. It germinates on new leaves and starts to initiate a secondary stage of infection. High rainfall and high relative humidities (above 70%), together with relatively low night temperatures (around 15°C), favor the progression of the disease. These conditions are prevalent at high altitudes. The disease affects plant productivity and yield only in specific cases. In general, it is considered as a late season disease of minor importance.
Sorry, to date we don't know of any biological treatment for Phaeosphaeria Leaf Spot. Please get in touch with us in case you know of anything that might help to fight this disease. Looking forward to hearing from you.
Always consider an integrated approach with preventive measures together with biological control measures if available. Fungicides such as mancozeb, pyraclostrobin can be sprayed on leaves to control the disease.