Myrothecium leaf spot

Fungal leaf spots

Pathogen

Myrothecium roridum.

Hosts

Lamium, Molucella, Rudbeckia and Salvia.

Symptoms

This disease causes leaf spots. Concentric rings may develop in the lesions. Raised, black sporodochia develop on diseased tissue. In high humidity, the sporodochia are encircled by a tuft of white growth.

Spread

Spores are splash-dispersed by irrigation water and rainfall.

Sporodochia on diseased tissue
Black, raised sporodochia on diseased tissue. Note that many are surrounded by a white tuft of spores.

Management

Avoid injuries to plants. Young or injured tissue is most susceptible. One common cause of wounding is packaging for shipping; disease readily develops following shipping. Avoid excessive fertilization – high fertilizer rates that favor lush foliage growth have also been associated with disease outbreaks. Reduce periods of leaf wetness by carefully timing irrigation. Fungicide applications may be needed to control severe disease problems.

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