Cercospora leaf spot of Cercis

The disease known as Cercospora leaf spot is caused by the fungus Pseudocercospora cercidis-chinensis. This pathogen is a specialized parasite that primarily attacks the foliage of its host, leading to physiological stress and reduced photosynthetic efficiency. While it is rarely fatal to mature trees, it can significantly compromise the aesthetic value and long-term vigor of infected specimens.

The primary host for this pathogen is the Chinese redbud (Cercis chinensis). The disease is most prevalent in nursery settings, urban landscapes, and garden environments where specific microclimates favor fungal growth. While it is host-specific, the severity of the infection can vary depending on the environmental stress factors acting on the individual tree during the growing season.

Symptoms initially appear as small, irregular, or circular spots on the leaf blades, ranging from light brown to dark gray. As the infection progresses, these spots may coalesce into larger necrotic areas. Under high humidity conditions, a distinct gray or olive-colored fungal growth, consisting of conidiophores and conidia, develops on the underside of the leaves, which is a diagnostic feature for identification.

The development and spread of Pseudocercospora cercidis-chinensis are highly dependent on warm, humid weather. Rain splashes and wind play a crucial role in the dispersal of spores from the ground to the lower foliage. The fungus overwinters in the fallen leaf litter, which acts as the primary reservoir for inoculum during the subsequent spring when conditions become conducive to new infections.

• Remove and destroy all fallen leaves in autumn to reduce the inoculum level.
• Ensure adequate spacing between trees to improve air circulation and reduce humidity.
• Avoid overhead irrigation, which creates the moisture needed for spore germination.
• Apply fungicides containing copper or systemic triazoles if symptoms appear early in the season.
• Maintain tree vigor through proper fertilization and watering to improve natural resistance.