Brown leaf spot of poplar

The disease known as brown leaf spot is caused by the ascomycete fungus Drepanopeziza brunnea, which specifically targets various poplar species (Populus spp.). This fungal pathogen is particularly devastating in nursery settings, where it can cause significant defoliation, leading to stunted growth and reduced vigor in young saplings.

The primary symptoms appear as small, circular, brown to dark-brown spots on the leaf surfaces. As the infection progresses, these spots may coalesce into larger irregular necrotic lesions. Infected leaves typically exhibit premature yellowing and eventually drop from the tree, often occurring in mid-summer, which significantly reduces the photosynthetic capacity of the host tree.

The lifecycle of Drepanopeziza brunnea is highly dependent on environmental conditions, particularly high humidity and frequent rainfall. The fungus overwinters primarily in fallen infected leaves as mycelium. In the spring, when temperatures rise and moisture is available, the fungus produces spores that are disseminated by wind and splashing rain to healthy foliage, initiating new cycles of infection.

The damage caused by this pathogen is substantial, especially in clonal plantations where genetic uniformity makes entire blocks susceptible. The reduction in leaf area decreases nutrient reserves in the tree, making it vulnerable to secondary pests and cold stress. Persistent defoliation over consecutive seasons can eventually lead to top dieback and overall tree decline.

• Removal and destruction of fallen leaves to eliminate inoculum.
• Selecting and planting resistant or less susceptible poplar clones.
• Improving stand aeration through proper spacing and pruning.
• Application of protective fungicides during the early leaf development stage.

Effective management requires an integrated approach focusing on sanitation and host resistance. By minimizing the amount of overwintering inoculum through leaf litter management, nurseries can significantly reduce the severity of early-season outbreaks and protect the overall health of the poplar stands.