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.