Mycosphaerella leaf spot of poplar

Mycosphaerella leaf spot of poplar is a fungal disease caused by the pathogen Mycosphaerella populicola. This condition belongs to the group of foliar diseases that primarily affects the leaves, leading to reduced tree vigor and significant aesthetic damage, especially in commercial poplar plantations.

The primary hosts of this fungus are various species within the Populus genus. The disease is particularly destructive in nurseries and young plantations, where high humidity and limited air circulation facilitate rapid pathogen colonization of new leaf growth throughout the growing season.

Symptoms typically manifest as small, brown-to-black necrotic spots on the leaf surface. As the infection progresses, these spots may enlarge and coalesce, often resulting in yellowing (chlorosis) of the surrounding tissue, premature leaf drop, and in severe cases, the potential for stunted growth of the woody parts.

Development is favored by cool, wet spring weather and periods of high humidity during the summer. The pathogen overwinter as specialized fruiting bodies on fallen leaves, which act as the primary inoculum source for the following season when spores are released via rain splashes and wind currents.

• Sanitation is key: rake and dispose of all fallen leaves during autumn;
• Select and plant resistant poplar clones to minimize the risk of infection;
• Improve air circulation through proper site spacing and pruning;
• Apply preventative fungicide sprays during the early stages of bud break if pressure is high;
• Monitor nurseries regularly to ensure early detection and immediate removal of infected seedlings.