May 1997

Bacterium Attacks Shiitake

While the May 1997 issue of The Mushroom Growers' Newsletter contains much more information, this page will help you identify and begin to take action immediately to prevent this disease on your farm. Our special thanks to John Donoghue and Northwest Mycological Consultants for doing the basic research that identified the cause of this disease and for helping us bring the information to you on this web page.

This diagram shows an infected mushroom and the key characteristics which will help you identify Burkholderia gladioli pathovar agaricola when it appears on your crop. The photos which follow display in graphic detail what this bacterium can do to an infected mushroom and your entire crop. Whether you have seen this disease on your farm or not, take the following advise from Northwest Mycological Consultants:

• Separate new and old blocks: Start your next crop in a clean room. Old blocks can harbor the organism and introduce it to your new blocks.
• Use Good Farm Hygiene: Get your old blocks away from your farm. Keep your farm clean!
• Remove diseased mushrooms: The organism multiplies rapidly once it gets a foot hold on your mushrooms.
• Dry down your fruiting rooms: Cut back on sprinkling by reducing air flow in your rooms to slow water loss from your blocks. Watch the dew point - condensation on your mushrooms can encourage bacteria.
• Break the population build up: Disinfect your soak water. Use a dry period in the fruiting cycle. Run quicker fruiting cycles. Water with disinfectants and dry your mushrooms quickly.
• Lower the levels of mobile vectors: Flies, mites, bugs and even people help spread bacteria. Do what you can to reduce their contact with your crop.

Infected mushrooms on later flush blocks. Note poor production, small size of mushrooms and evidence of disease on all mushrooms and pins. (Disease does not show symptoms on first fruiting.)

Infected mushrooms showing browning of gills from the stipe out. These mushrooms have brown sunken lesions on the tops of their caps, have hollow areas at the tops of their stems and have matured early.

Progress of the disease from small pins to maturity. Note dark sunked superficial lesions in the center of the caps, small size of the early matured mushrooms, brown gills and contorted cap margins - uplifted in age.

Dark sunken superficial lesions with pits extending to the stipe. Stems often hollow and browning near the cap. Caps easily knocked off their stems at cap/stem transition.

If you think you have this disease on your farm, please contact Northwest Mycological Consultants and tell them what's happening. The firm is tracking the extent of the disease and collecting cultures of the bacterium. The information they develop will benefit all shiitake growers.

The photos and most of the text used on this page are ©1997 by Northwest Mycological Consultants and used here with permission.