Cause An oomycete, Pythium oligandrum, which forms durable resting spores resistant to heat (can withstand 194°F for 60 minutes). Problems develop when this fungus-like organism is present before spawning or introduced with the spawn; it does not seem to cause disease when introduced a couple of days after spawning. Pythium is commonly found in soil or associated with plant roots and is enhanced with wet soil conditions. Pockets of high nitrogen may favor Pythium growth.
Symptoms Discrete regions, an irregular oval in shape, with a black color and lack of fungal crop growth. These patches can extend deeply into the spawning medium. Eventually the mushroom crop will grow into the black regions but crops can be suppressed in the first harvests.
- Avoid contamination of the growing media with raw soil.
- Avoid water run-off into production area.
- Mix supplements well into the mushroom-growing medium.
Reference Fletcher, J.T., White, P.F., and Gaze, R.H. Mushrooms: Pest and Disease Control. 1989. Intercept Limited, Andover, Hants, England. 174 pp.