Tree Leaf Blight

Cause

• Leaf blight or leaf spots are the most frequent foliar disorder of ornamental and shade trees caused by numerous fungi. Leaf blights have different names, often identified by the name of the disease causing fungus. Pathogenic fungi are the most frequent cause of leaf blight or leaf spots. Common names include anthracnose, white mold or downy spot, black spot, leaf blister, ink spot, shot-hole, scab and tar spot.

Disease Cycle

• The fungi that are responsible for the disease overwinter under the trees in the fallen foliage. The infection-causing spores are activated during the moist, early spring climate, just as the weather starts to warm up. Carried to the new foliage with splashing water and air, the spores penetrate the wet leaves, germinating and leading to the infection. Under the effects of gradually warming weather and with moist conditions, the infection spreads throughout the tree and to other plants in the area.

Damage

• Though certain symptoms of leaf blights are exclusive to the specific causal agent, leaf blight generally causes discoloration on foliage that ranges in size from a pin head to larger areas that cover the entire leaf. The discolored patches or spots are black, tan, brown or reddish in color, raised or shiny, and often have purple or red outer margins. Fungal fruiting bodies, or reproductive spores, are often seen within the discolored areas on foliage, in the form of black dots. Infected foliage yellows and drops and overall tree vigor is affected. Certain fungi also damage flowers, buds and small tree branches.

Control

• Trees that are in good health, with regular irrigation and fertilizing are less prone to infection from disease causing fungi. Newly transplanted tree and those that are already suffering from a pest infestation are also more susceptible. Use recommended fungicide as protective strategy for best efficacy. Spray the trees first at bud break and follow with another application two weeks later. A third application is often required in areas with heavy spring rains. Recommended fungicides include products containing mancozeb, maneb or chlorothalonil.