Phyllosticta Leaf Spot

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• Phyllosticta minima (Phyllosticta leaf spot)

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Dothideomycetes
Order	Botryosphaeriales
Family	Botryosphaeriaceae

Scientific Name

Phyllosticta

Common Name

Phyllosticta leaf spots

Author:Name, Organization

Reviewed by:Name, Organization

Asexual stage: Phyllosticta spp.

Hosts

Boxelder, and other maples

Diagnosis and Damage

Phyllosticta leaf spot damage.

This leaf spot fungus produces lesions on the leaves that are round or nearly so, up to 8 mm across, yellowish brown or purple at the edges, and pale yellow in the center, where they become thin and translucent. Each lesion is bounded by a very narrow ridge. The fragile central tissue often breaks out, leaving a ragged hole. Severe outbreaks may impart a distinctly yellowish color and sparseness to foliage in tree crowns viewed from a distance.

Biology and Disease Cycle

The pathogen survives winter in fallen leaves and, in spring, produces spores that are dispersed to new foliage, starting another cycle of disease. The spores are adapted for dispersal by water rather than by wind. This explains the increase of disease during rainy seasons, and explains why this pathogen is not normally a problem in this regions semi-arid climate. After infection, the host leaf is initially defenseless but soon localizes the infection within a small area. Thus, even if infections are numerous, they usually cause no great loss of photosynthetic surface unless they trigger abscission (leaf drop).

Management

Management options include collection and disposal of infected leaves in the fall to lower the amount of inoculum present to cause infection the next year. Pruning of host plants to encourage good air movement through the canopy, promoting rapid evaporation of free water. Applying fungicides prior to infection is probably only needed in extreme cases.