Myrothecium leaf spot

Myrothecium lesion on New Guinea impatiens leaf

Myrothecium lesion on New Guinea impatiens leaf

Multiple sporodochia

Multiple sporodochia

Raised Myrothecium sporodochia on leaf surface

Raised Myrothecium sporodochia on leaf surface

Lesion on New Guinea impatiens leaf

Lesion on New Guinea impatiens leaf

Ring spot on New Guinea impatiens leaf

Ring spot on New Guinea impatiens leaf

Myrothecium lesion with tuft of spores

Myrothecium lesion with tuft of spores

 Pathogen: Myrothecium roridum

Hosts: Lamium, Molucella, Rudbeckia, Salvia, New Guinea impatiens

Symptoms: This disease causes leaf spots, concentric rings may develop in the lesions. Raised black sporodochia develop on diseased tissue. In high humidity sporodochia are encircled by a tuft 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 of perennials 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. Minimize periods of leaf wetness through careful timing of irrigation. Fungicide applications may be needed to control severe disease problems.