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Test your knowledge about Bacterial Blotch (Brown Spot/Brown Blotch)

Evaluate yourself! How well do you know the causes, symptoms, prevention, and treatment principles of bacterial blotch on mushrooms?

Learning resources to pass this quiz: Bacterial brown blotch disease on mushrooms

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Questions covered in this Quiz

Definition - What is Brown Blotch disease?

Possible answers:

  • A bacterial disease that mainly affects mushroom quality / appearance
  • A fungal pathogen that turns brown when it sporulates
  • A human pathogen that makes mushrooms unsafe to eat and even touch
  • A nutrient deficiency that only happens in outdoor grows

Pathogen - Which species of bacteria is most associated with Bacterial Blotch disease on mushrooms?

Possible answers:

  • Pseudomonas (especially Pseudomonas tolaasii)
  • Bacillus (especially Bacillus subtilis)
  • Lactobacillus (especially Lactobacillus plantarum)
  • Streptomyces (especially Streptomyces griseus)

Case study - Is there something wrong with the mushroom caps?

Possible answers:

  • Bacterial blotch on caps
  • Normal caps, just slightly deformed

Practical case - Imagine you noticed signs of bacterial blotch on mushroom caps in your monotub. What are the possible actions?

Possible answers:

  • Dry water drops on mushrooms (avoid hard fanning)
  • Reduce humidity to 80-85%
  • The WD-40 trick to prevent water droplets from the lid from falling on the mushrooms
  • Treatment with 150-250 ppm chlorinated water
  • Treatment with antibiotic spray
  • Wash up mushroom caps with clean filtered water and let them dry
  • Maintain a stable humidity of 95-99% to prevent caps from cracking
  • Treatment with fungicide spray

Symptoms - What may bacterial blotch look like on the cap surface?

Possible answers:

  • Wet, slightly slimy brown spots
  • Dry brown speckles and pits
  • Fluffy cotton-like growth on mushroom caps
  • Dry black spots on mushroom caps
  • Ink-like slime on mushroom caps
  • Inverted caps, resembling a rose (or gills growing on caps)

Safety concerns - Is it safe to harvest mushrooms with the signs of mild Brown Blotch on their caps / stems?

Possible answers:

  • Yes, just dry mushrooms properly (bacterial cells can't thrive without water); toss heavily contaminated (rotted) mushrooms
  • No, throw away ALL contaminated mushrooms, even with tiny brown spots

Rough time window & Brown Blotch risk - Blotch risk increases when water stays on caps / stems for…

Possible answers:

  • 30 minutes
  • 4–8 hours and longer
  • Even 2–3 minutes is enough to trigger the brown blotch
  • 3 days

Contamination vectors - What do you think are the 2 main vectors for the spread of bacterial spot when growing mushrooms at home?

Possible answers:

  • Bulk and Casing substrates
  • Air (spores in the air)
  • Insects
  • Contaminated genetics (spore print, spore syringe or liquid culture)
  • Grower (hands, clothes, hair)
  • Tools
  • Water / humidity (spreading by misting or humidifier)
  • Grain spawn

Practical case - What can lead to bacterial blotch?

Possible answers:

  • Direct heavy misting onto fruit bodies (especially large droplets)
  • Fogger/humidifier running too long without enough fresh air exchange
  • Water pools on the substrate surface after misting
  • Temperature/humidity swings that increase condensation (including lid drips)
  • Using a heat mat under the fruiting chamber
  • Intense ventilation / fanning
  • Overheating in incubator during bulk colonization perid
  • Opening the fruiting chamber too often

Heavy Pseudomonas contamination - What should you do with heavily contaminated mushrooms (more than 50% of the cap is rotten)?

Possible answers:

  • Remove and toss heavily affected mushrooms to reduce spread to nearby mushrooms
  • Ignore it; blotch always resolves by itself

Treatment - Spot treatments with 150-250 ppm chlorinated water work best when…

Possible answers:

  • Mushroom caps are dry (not covered in droplets)
  • Caps are visibly dripping wet
  • The grow is kept at maximum humidity with constant fogging
  • You apply treatment preventatively before any symptoms appear

Condensation control - The article describes a “WD-40 trick” to reduce droplets falling onto mushroom caps from the fruiting chamber lid. What’s the intended effect?

Possible answers:

  • Creates a film, that make droplets smaller and more adherent (sticked to the lid) and prevents them from dropping onto mushrooms
  • Increase droplet size, so they move to the walls of the fruiting chamber and prevents them from dropping onto mushrooms
  • Turn condensation water drops into gel that stays on the lid and and prevents them from dropping onto mushrooms
  • Eliminate all humidity from the fruiting chamber and helps to dry out condensation and water drops on mushrooms faster

Case study - What do you think about these mushrooms?

Possible answers:

  • Bacterial blotch on caps after drying
  • Normal caps with cracks due to low humidity environment

Case study - Bacterial blotch?

Possible answers:

  • Yes, it's bacterial blotch on cap
  • No, it's mutation (rosecomb)

Case study - "First timer. Hillbilly strain." Are the caps (in blue circles) fine?

Possible answers:

  • Absolutely fine, just a genetic feature (phenotype)
  • It's mild bacterial blotch on caps

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