Symptom Identification and Control Methods for Leaf Spot Disease on Japanese Spindle (Euonymus japonicus)

Symptoms: The disease affects the young and old leaves of Japanese spindle (Euonymus japonicus). Yellow-brown spots appear on the upper surface of the leaves and expand into nearly circular or irregular shapes, 4 mm to 14 mm in diameter, with a grayish-white center, light brown concentric rings, and a dark brown slightly raised edge. Dense tiny black mold dots form within the lesions. The spots show through to the underside, though the color on the underside is slightly lighter than on the upper surface. After the lesions dry up, they crack apart from the healthy tissue, eventually forming holes. This often causes early leaf drop.

Pathogen: fungus, Cercospora destructiva Rav. of the order Moniliales, class Hyphomycetes, subdivision Deuteromycotina.

Disease pattern: The pathogen overwinters in diseased leaves on the tree and on the ground. In spring, it produces conidia for primary infection, and thereafter produces large numbers of conidia throughout the growing season for multiple secondary infections. When there is abundant rain, high humidity, freezing damage in spring, or when plants are too densely planted with poor ventilation, the disease tends to be severe and cause leaf drop.

Control methods

Maintain good sanitation in green areas. In winter and spring, sweep up fallen diseased leaves and burn them in a centralized manner.

At the early stage of the disease, spray 1:2:200 Bordeaux mixture, or 70% thiophanate-methyl wettable powder at 1000 times dilution, or 65% zineb wettable powder at 600 times dilution, and then spray 1 to 3 more times depending on the severity of the disease.