PPDL Picture of the Week

February 6, 2017

Myrothecium diseases in the greenhouse

Tom Creswell, Diagnostician/Director, Plant and Pest Diagnostic Laboratory

Myrothecium roridum is a fungal pathogen that may cause leaf spots, stem cankers and dieback on a wide range of plants when conditions are favorable in the greenhouse. This disease is often when greenhouse humidity is very high, such as during propagation or when young plants are grown in crowded conditions early in the spring.  Injuries during handling and transplant and high fertilization rates can both increase susceptibility to infection.

Symptoms may include crown rot, leaf damage (shown Figures 1 and 2 on Lindernia anagallidea), stem dieback (shown in Figures 3 and 4) and/or stem canker (shown in Figures 5, 6 and 7).  We see this fungus most often on young perennials and herbs but it may also attack woody plants such as Euonymus and annuals such as begonia, petunia, verbena and impatiens.

Infected material should be removed from the greenhouse and benches, tools and pots sanitized to reduce spread. Reduced humidity and increased space between plants can also help reduce spread as can application of appropriate fungicides.