MUSHROOMS are scientifically defined as the fleshy spoor-producing body of any various basidiomycetous fungi, typically consisting of a cap or mushroom head (pileus) at the end of the stem arising from an underground mycellus.
The most common diseases of mushroom include bacterial blotch, green mould, die-back disease, dry bubble disease and wet bubble disease.
Bacterial blotch (pseudomonas tolaasi)
The main source of bacterial blotch in the mushroom farm is the casing soil.
The disease is favoured by dampness; high humidity, high temperatures (over 20 degrees Celsius and poor ventilation in the growing houses.
It can be spread by the workers’ hands, irrigation water and on the inventory.
Mushroom flies and mites also spread the disease.
The first disease symptoms appear in areas of caps that have been moist for the longest time and areas where mushroom caps touch.
Symptoms include spots that darken becoming chocolate-brown and slimy.
It can also cause distortion and splitting of the stripes.
When infection is severe, spots spread throughout the whole mushroom surface.
Seriously diseased mushrooms can become deformed and the caps can decay giving a foul (unpleasant) odour.
Young pins affected by the disease become brown and do not develop further .
What to do:
l Maintain strict hygiene and sanitation in mushroom facilities
l Use properly prepared substrate and casing soil that have been adequately pasteusterised
l Avoid excessive humidity, high temperatures and poor ventilation in growing rooms
l Avoid fluctuation of temperatures in the growing rooms which may cause water condensation on mushroom caps
l Remove diseased mushrooms which can be a source of the disease
l Control mushroom flies and mites which can spread the bacteria
l Water mushrooms with chlorinated water (125ml, 10 percent chlorine solution for 100l of water per 100 square metres).
Use calcium hypochlorite products since sodium hypochlorite may burn caps before first break when the pin size is four to five millimetres
l Remove spent substrate from the farm. It can be used as manure for other crops
Green mould (trichoderma aggressivum)
This fungus is soil-borne.
There are many species of the fungus but trichoderma harzianum biotype 4 (Th4) is a major problem, particularly to button mushrooms.
It gains entry to growing rooms primarily through contaminated personnel and equipment.
Other sources include poorly composted substrate or carryover in rooms that were not sufficiently steamed off.
Once introduced, it rapidly spreads into large disease areas from infection source.
Infection of casing soil can result in serious losses.
Green mould is characterised by dense white mycelial growth followed by extensive green patches on casing or compost or mushroom caps.
The spores of the fungus are sticky and can easily be spread by flies, mites and workers to previously uninfected area.
Red pepper mites are often associated with the disease.
What to do:
l Maintain hygienic conditions at all stages of production
l Use properly prepared substrate and casing soil that have been adequately pasteusterised
l Remove contaminated substrate as soon as possible from the farm and dispose of it at a considerable distance not less than 100m
l Control flies and mites
l Spread table salt on the compost in affected areas when green mold is first seen.
l Filter air to prevent colonisation of sterilised compost
l Disinfest all structures and equipment
Die-back disease
It causes spots in the casing soil where no mycelial growth occurs.
Around these spots, mushrooms of low quality appear with long stems and dirty caps.
Sometimes the only indication of a virus infection is low yield.
In severe cases, a few deformed mushrooms are produced.
The disease can be introduced to the farm by infected spawn.
It is spread by spores and mycelium from infected mushrooms.
Mushrooms affected with the virus open fast, releasing infected spores. Sometimes, mushrooms that were formed inside the casing layer come out already open.
Spores from infected mushrooms are easily carried by wind, insets, on implements, clothes and hands of personnel.
What to do:
l Maintain good sanitation and hygiene in growing rooms
l Use well prepared and pasteurised substrate (compost)
l Control flies and mites
l Workers should dip their shoes in a disinfecting solution (sodium hypochlorite) (household bleach) before entering the growing rooms
l Remove spent substrate from the farm. This can be used as manure for other crops
Wet bubble (mycogone perniciosa)
This disease, like dry bubble, is soil-borne.
Infested soil may be primary source of infection.
Infection usually occurs at casing.
The disease is spread within a house mainly by water splash, on clothing, equipment, flies or mites.
Cross-contamination between houses can also take place.
Young pin heads infected by mycogone grow into shapeless lumps, cauliflower-like, which have a velvety appearance initially and eventually break down producing small amber droplets of liquid on the surface.
It can also appear as gray fuzzy growth on gills; a series of radially arranged (from the centre) flat surfaces located on the underside of the cap on which spores are formed. – Source – Agribusiness Information Portal