Describe the change
Yellow, ginger or brown lesions on the cap.
Bacterial diseases
Ginger, yellow and other bacterial blotches
“Ginger blotch” and “yellow blotch” describe appearances, not a dependable field identification of one bacterium.
Organism / cause: Multiple Pseudomonas lineages; species cannot be read from cap colour
Where this evidence applies: Blotch-associated isolates from Agaricus in Western European research.
Picture → observation → next check
A visual guide to your observations
- Cap surface
Record a local spot versus whole-cap colour, and whether it was present before picking.
- Gills underneath
Separate normal maturity-related pigmentation from unusual wetness, exudate or deterioration.
- Inside the stem
Internal changes can differ from the outside. Obtain sampling instructions before cutting suspect material.
- Casing and compost
Note whether the change starts in the fruit body, the casing surface or the substrate below.
Keep another explanation open
P. tolaasii blotch, mechanical injury and residues.
Collect one useful piece of evidence
Use neutral-light photographs and record picking/packing timing.
A visual match is only a starting point. Molecular characterisation and disease testing underpin the published classifications; a visual match is weaker evidence.
01 · Observe
What you may see
- Yellow, ginger or brown lesions on the cap.
- Similar colours arising in different batches or under different wetness conditions.
No verified reusable diagnostic photograph is included for this entry. The illustration above explains observation context, not a confirmed disease specimen. Consult the original source figures where available.
02 · Compare
What can look similar
- P. tolaasii blotch, mechanical injury and residues.
- Ageing or pigmentation of the cultivated strain.
How it may arise or move
Wet surfaces and handling are investigation priorities; different isolates can behave differently.
03 · Check
Collect evidence before changing the crop
- Use neutral-light photographs and record picking/packing timing.
- Ask whether lab findings demonstrate pathogenicity rather than only detecting a bacterium.
What confirmation needs: Molecular characterisation and disease testing underpin the published classifications; a visual match is weaker evidence.
Use the field record and sampling checklist →04 · Respond
What to do next
- Treat the description as provisional and segregate affected lots.
- Do not choose antibiotics, phages or disinfectants from a colour chart.
These are investigation and containment steps, not a guaranteed cure. Do not eat, sell or distribute suspect material on the strength of a visual match. Do not culture unknown contaminants or experiment with pesticides in a growing room.
05 · Learn
Reduce recurrence
- Review cap-wetness control and hygiene.
- Retain lot history so recurrence can be compared meaningfully.
After intervention, compare new affected units, crop condition and inspection results against the same recorded baseline. A lack of visible growth does not, by itself, verify decontamination or food safety.
Read the stage-by-stage prevention plan →Evidence & sources
2020 molecular research; not an India-specific prevalence survey.
- Molecular characterization of Pseudomonas from Agaricus bisporus caps reveal novel blotch pathogens in Western Europe ↗
Research article indexed in PubMed · 2020
Used for: Blotch can involve several Pseudomonas species; molecular and pathogenicity testing.
Limit: Abstract and figure captions reviewed. Cap colour cannot distinguish the organisms.
- Genomic Characterisation of Mushroom Pathogenic Pseudomonads and Their Interaction with Bacteriophages ↗
Research article, PMC · 2020
Used for: P. agarici gill disease and P. tolaasii blotch distinctions.
Limit: Experimental phage results are not a farm treatment protocol.
Compare related explanations
Bacterial diseases
Brown bacterial blotch in button mushrooms
Persistent surface wetness can favour bacterial blotch. Managing cap drying means balancing the crop environment, not simply drying the entire room.
Agaricus caps; a brown spot does not establish bacterial identity.
Signs, checks & response →Bacterial diseases
Drippy gill
The gill surface matters: some disease is hidden beneath the cap. A cap-only photograph can miss the most useful evidence.
Agaricus bacterial gill disease.
Signs, checks & response →Environmental disorders
Rosecomb, residues and chemical injury
Unexpected forms or lesions after cleaning, spraying or nearby fuel use need an exposure history as well as a disease differential.
Rosecomb is classically described in Agaricus; broader crop filters cover exposure investigation, not identical symptoms.
Signs, checks & response →