Scouting for diseases: Myrothecium leaf spot

Jan Byrne, Michigan State University Extension, Diagnostic Services - May 22, 2009

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

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.

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.

Editor’s note: The information in this article is from MSU Extension publication E-2981, A Pocket Guide for IPM Scouting in Herbaceous Perennials. The publication can be ordered through MSU Extension: http://ipm.msu.edu/perennials.htm

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

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