Pleiochaeta leaf spot

The disease is caused by the fungus Pleiochaeta albiziae, a pathogen specifically targeting woody legumes. This fungus survives in plant debris and soil, acting as a primary source of inoculum for subsequent seasons. It is a persistent pathogen that requires integrated management strategies for successful suppression in garden and nursery settings.

The primary hosts of this pathogen are members of the Albizia genus, most notably Albizia julibrissin. While the impact is most visible on these ornamental trees, the fungus can also affect related legume species under favorable environmental conditions, leading to significant foliage damage.

Initial symptoms include the appearance of small, irregular brown or dark grey spots on the foliage. As the disease progresses, these lesions expand, often merging to cover large portions of the leaf surface. Under high humidity, mycelium and sporulation may become visible on the undersides of the affected leaves.

The development of Pleiochaeta albiziae is highly dependent on moisture and humidity. Spores are primarily disseminated by splashing water, rainfall, and wind. High-density planting without proper airflow promotes microclimates that are ideal for the rapid spread of the infection throughout the tree canopy.

Management of the disease involves a combination of sanitation and chemical controls. Removing fallen leaves is crucial, as the fungus overwinters there. Additionally, providing proper space between trees and avoiding overhead irrigation can significantly reduce infection risk. Fungicides containing copper or systemic active ingredients are effective when applied preventively during the growing season.