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La France disease of cultivated mushrooms | AG0518 |
Gisele Irvine and Jane Moran, Knoxfield
November 1999 |  |
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Introduction
La France disease is thought to be caused by one or more viruses. It is one of the most serious diseases of the common cultivated mushroom. Severe infection significantly reduces yield and can lead to complete crop failure. This disease occurs worldwide and can be difficult to control and eradicate.
Symptoms
The most noticeable and consistent symptom is reduced cropping, associated with one or more of the following: bare patches on the beds, long-bent stalks with small caps, premature opening of mushrooms, stalks tapering towards the base of stalk, and dying pinheads (Figure 1). Infected mycelium grows slowly in the beds and in areas where fruiting bodies are not produced.
In general, infection of the crop at spawning can lead to a higher level of disease and greater crop losses than infection at later stages.
Figure 1: Various symptoms shown by mushrooms infected with virus disease. Healthy mushrooms in the top centre of illustration.
Spread and source of infection
Infected mushroom spores are the most likely and common means of spreading the disease. The infected mycelium from previous crops can also survive in the mushroom trays and transmit the disease to new mycelium of the next crops. Mushroom sheds can also release infected spores into the farm system from clean-up procedures. Dust from around the farm may introduce infected spores into the spawning or growing rooms. Growing "flats" can also release infected spores into the surrounding room; one mushroom cap can produce 1 300 million spores and it is thought that only 10 infected spores are required for a disease outbreak to occur.
Host range
Cultivated mushroom, Agaricus bisporus.
Control
Strict farm hygiene is the best means of prevention. The following management and hygiene practices can help control the disease:
Critical stages in cropping
Phase 1 & 2
Maintain 60oC temperature throughout the compost to kill mushroom spores. If infection occurs on phase 1 stacks, and if peak heat (phase 2) is inadequate (thermal death point of mushroom spores equals 65oC for 16 hours), then spores may survive. Filter air and seal rooms properly to prevent mushroom spores from entering the peak-heat room during cooldown.
Spawning (high risk stage)
- Clean equipment thoroughly.
- Ensure workers have clean-spare clothes (decontaminate for 30 minutes in tumble drier at warmest setting).
- Ensure absolute filters are fitted to spawn-run buildings.
- Clean trays to prevent infecting clean mycelium with old-infected mycelium.
Spawn-run
- Prevent infected spores or mycelium entering room via poorly filtered air, insects such as phorid or sciarid flies and on staff clothing.
Casing
- Keep casing ingredients free of contaminants.
- Clean equipment thoroughly.
- Ensure workers have clean clothes during casing operations.
- Assess cacing (term used for mushroom production method) or ruffling critically as both can spread infected mycelium.
Cropping
- Infection at this stage does not usually cause significant losses, but "flats" can produce infected spores which may threaten subsequent crops.
Cookout and cleaning up
- Kill and remove living mycelium and spores (70oC for 12 hours will kill mycelium and spores).
General hygiene
- Use strict hygiene practices for filling/casing and spawn-run areas.
- Ensure that staff working in cropping area enter the spawning/casing area with clean clothes.
- Disinfect the change room daily.
- Clean workshops, storage rooms and alleys regularly.
- Dispose of old boxes and other miscellaneous items as they collect dust.
- Clean concrete areas daily.
- Clean boxes returned from cannery.
- Wash down forklifts.
- Use and replenish footbaths outside each room every day.
- Maintain fly control as they may carry spores.
- Clean inside-mixing boxes and air-conditioning units at end of every crop.
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Tests available
The Institute for Horticultural Development's diagnostic service provides you with two testing procedures which:
- Monitor levels of virus like particles in a crop (ISEM test).
- Detect La France disease in spawn and the crop (RT-PCR test).
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Illustration (Figure 1) supplied by Department of Agriculture NSW.
Correct diagnosis is essential for effective pest and disease control. A commercial diagnostic service is available at the Institute for Horticultural Development (IHD). For further information phone Crop Health Services on (03) 9210-9222 or fax (03) 9800 3521.
For further information on registered chemicals, phone Chemical Information Service
This publication may be of assistance to you but the State of Victoria and its officers do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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