Trichoderma, as most of us know it (top left), and magnified many times.

Last month I wrote a long article on Trichoderma. Not much new but many points, hopefully of interest. The last page unfortunately got lost; it gave a list of recommendations for growers. The omission gives me the excuse to expand
this half page to a full article, detailing this advice more fully and emphasising some points in heavy print. In my opinion most serious green mould outbreaks are now due to cross-contamination by Trichoderma, type Th2 on farm. My reasons were outlined.

Eliminate dust, at least prevent it getting into new houses.
Trichoderma has slimy spores, not easily airborne, except on dustparticles. Dust may comprise dry, dead, red-pepper-mites, or particles of dry casing/compost. Outbreaks of green-mould are much more frequent after dry, windy weather, for example in autumn.
A solid entrance drive, i.e. concrete, can be washed and if bordered by grass, dust is trapped. A drive made of stones grinds spilled compost into dust with every passing vehicle. Aim for firm washable surfaces, try to eliminate spillage of compost, particularly if spent. Bags/blocks allowed to dry, prior to emptying create most dust. Lightly watering helps prevent this. If bags are dry when tossed into a skip, or blocks are dry when shovelled in, clouds of dust are created. The further compost falls, the more the impact and the greater the dust. Assuming this settles and it doesn't rain, it may be blown through an open doorway onto a new compost fill, or onto the plastic of an arriving load, even several days later.

Remember polythene attracts dust and that some dust on the outside of bags will be transferred by hand to the inside, particularly at levelling. If the farm tends to have a green-mould problem, level the bags early by
pressing on the outside of the bags i.e. not touching the compost. This may have to be done early before the compost has become woven with mycelium. Or, level late when compost is less easily Th2 colonised.Both bags and blocks have 'breathing' holes. If watering over them is used to beneficially keep compost from drying out, dust may be carried inside, via
the holes. Avoid such humidity spraying if there is a Trichoderma problem on farm.

If dust is contained within the growing-house, by confining the emptying operation indoors, then the ventilation system becomes highly contaminated.This will need thorough cleaning prior to refilling, including the crevices of the radiator grill and air-straightener.
Do not use formaldehyde as a disinfectant, it appears to encourageTrichoderma.

Spawn run Temperature

Keep spawn-run temperatures as low as possible i.e. not higher than 25C. This will favour Agaricus and disadvantage Trichoderma. If humidity spraying by watering or misting is used to keep temperatures down,
remember this could, transfer spores inside.
There is a temperature surge, usually around day 8-10. Cool to 22-23C just prior, so that when the surge comes it does not get out of control. High yielding compost is most prone to Th2 probably because the spawn-run is warmer.

Mites
If red-pepper-mites are noticed, it is likely that they have fed and multiplied on Th2 mycelium. By the time they are seen they may have so reduced the amount that green sporulation never develops. Nevertheless Th2 may have caused damage by slowing the growth of Agaricus. This explains why some
bags with mites are never productive, despite vigorous Agaricus mycelium seen in the bag.
Mites swarm and move to the highest vantage point. They tend to get everywhere, a high proportion carrying Th2 spores. Never lift mite laden bags, mites transfer to clothing. Even in the skip they will move up the sides or to the highest point. From this they may blow into a 'new' house. Covering a bag with another bag is beneficial, provided mites don't get on
clothing. Spraying bags with Malathion or Kelthane may drive mites down. However, using these chemicals is now illegal in mushroom houses and if detected would cause a scandal.

To remove mites. Cut a disc of cardboard a bit smaller than the diameter of a bag, about 40cm (16 inches). Place this on an old newspaper and cut round with scissors to produce a stock of paper discs. Place a disc centrally on a bag with mites and most will quickly transfer to its upper surface. Pick up such discs with tongs, drop in a bin-bag and quickly bum, somewhere outside
Mites can be washed down a drain or under the bottom edges of the polythene cover, without killing them. Many will crawl out again. Another problem is Th2 mycelium and mites getting into the tubing used for racking. A good method of killing mites, etc. is by cooking-out.
Clothing and preparation for levelling
Woollen garments tend to be destroyed by frequent or hot washing, they are inappropriate for use on a mushroom farm.
The most damaging Th2 outbreaks begin at the start of spawn-run. Th2 can grow across damp polythene 2.5cm (1 inch) a day. It is appropriate to think of levelling as a surgical operation, requiring clean clothing, scrubbing down, cleaning even ~ door handles. A well distributed pinhead size spot of green could affect a whole house. Some growers obviously don't realise
this. Two weeks ago I saw a grower stick his finger through the plastic side of a bag, look at it, say 'yes that's green' then put his hand back into his pocket!

The worst Trchoderma cases follow use of compost as CACing, Compost should not be used for CACing.
Check your casing supplier is hygiene conscious, clean and disinfect any surfaces that casing is going to touch, look out for any dust sources and wet them down. Low level contamination at this stage may only lead to a small amount of green on the casing but for the next house this could be the
source of enough contaminated dust to produce a wipe out!