PPDL Picture of the Week

September 12, 2016

Horsechestnut Leaf Blotch

Gail Ruhl, Sr. Plant Disease Diagnostician, Dept. of Botany and Plant Pathology, Purdue University

The blighted areas visible on horsechestnut leaves are symptoms of the common fungal disease called Guignardia leaf blotch. The disease affects several species of horsechestnut and buckeye (Aesculus species). Fr​om a distance, infected trees appear to be severely scorched.  On closer inspection, reddish-brown leaf spots with bright yellow margins become obvious. The spots enlarge and blotchy areas covermost of the leaf surface; infected leaves often drop prematurely. This fungal disease can be distinguished from environmental leaf scorch by the presence of tiny, pin-head sized, black, fruiting bodies formed by the fungus within the leaf blotches. The fungus overwinters in these fruiting bodies on fallen, infected leaves. To to reduce the amount of fungus present the following season, rake and remove fallen, blighted leaves.

Even though the symptoms are quite noticeable, the impact of this disease on tree health is minimal since severe symptoms develop relatively late in the growing season. Fungicide applications may be warranted in nurseries, butare not recommended for home landscapes.

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