LaFrance virus disease

Of all the diseases confronting mushroom growers, none have been the subject of more confusion than viral diseases. Viral diseases can be confused with the effect of poor cultural practices or the bacterial disease mummy. Since no known commercial mushroom strain is resistant to viruses, growers must incorporate preventive measures into the IPM plan and rigorously carry out control measures.

The virus lives in mushroom spores and mycelium (spawn). Infected spores spread the disease to other new crops. Infected mycelium (spawn) may survive in the bed boards or quickly spread in bulk phase III facilities. Spores survive many years and can be released during farm renovations.

Symptoms (Figure 1-4):

• Portabellas don’t size up; lower yield, Fig 1.
• Bare areas with few pins and mushrooms, Fig 2.
• Premature opening of the veil (small caps)
• Mild yield loss

Severe infection:

• “Drumstick” (small caps, long stems) Fig 3.
• Weak growth in the casing that often disappears over time
• Die-back of mycelium in the compost, Fig 4.
• Stems discolor quickly when cut
• Significant yield loss

Control:

• Exclude, eradicate, or reduce inoculum.
• Mushroom spores at spawning
• Mushrooms should be harvested before they mature and the caps open, releasing spores.
• Infected mycelium at spawning or casing
• Isolate the crop.
• Regularly scheduled replacement of filters/filtration
• Air movement—high positive pressure in spawning and casing areas
• Practice postharvest steaming to eliminate pathogens and mushroom mycelium/spores between crops.
• Virus-infected mycelium in the wooden tray/bed boards
• Virus-infected mushrooms and spores left on the bed

figure 1

figure 2

figure 3

figure 4

Bacterial diseases

1)  Bacterial Blotch

Signs and Symptoms:

• Superficial discoloration which leads to lower quality in the marketplace
• First pale yellow, then darkens to golden yellow to brown color.
• Bacterial pathogen: Pseudomonas tolaasii, recently other species have been found to cause similar symptoms

2)  Mummy Disease

Signs and Symptoms:

• Stunted growth, swollen base
• Sometimes mushrooms develop curved stipe with translucent, longitudinal streaks on the side
• Tissue appearance: spongy, dry and leathery
• First break can be harvested; second break mushroom does not grow in the affected area
• Scientific name: Pseudomonas species

By David M. Beyer, Penn State University