P&PDL Picture of the Week for
September 11, 2006

Guignardia Leaf Blotch

Karen Rane, Sr. Plant Disease Diagnostician, Dept. of Botany & Plant Pathology, Purdue Univ.

The blighted areas on these horsechestnut leaves are symptoms of the common fungal disease called Guignardia leaf blotch. The disease affects several species of horsechestnut and buckeye (Aesculus species). Symptoms first develop as light green or yellow blotches or spots, which become reddish-brown with yellow margins as the lesions mature. Blotches may cover
most of the leaf surface, and affected leaves often drop prematurely. The fungus overwinters on fallen infected leaves, and spores from leaf debris are splashed onto developing new foliage and cause initial leaf spots each spring. Spores are produced in leaf lesions throughout the summer, causing repeated infections.

While 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, but
are not recommended for home landscapes.

For more information on this disease, see the following link: Guignardia Leaf Blotch - UMass Extension





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Guignardia Leaf Blotch

Figure 1. Horsechestnut tree showing large areas of browning foliage due to Guignardia leaf blotch.

Guignardia Leaf Blotch

Figure 2. Blighted horsechestnut leaves.

Guignardia Leaf Blotch

Figure 3. Close-up of horsechestnut leaf showing brown blotches with yellow margins.

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service