A Story From the Field: The Grow House That Stopped Smelling of Mushrooms

Uncle Serm and Auntie Boonma have grown grey oyster and Hungarian oyster mushrooms for almost fifteen years on a small farm in Bang Len district, Nakhon Pathom, not far from the Tha Chin River. The farm has three grow houses made of thatch and shade netting, each packed with bamboo racks holding thousands of cultivation bags. At the front there is a small packing room where the family weighs and bags the harvest every morning for the market, and a few dozen metres away stands their raised wooden house.

During the 2026 floods, water from the surrounding fields and canals poured into the farm. It rose almost to the bottom shelf of the racks and stayed for nearly two weeks. When it finally drained away, Uncle Serm walked into the first grow house and stopped dead. The air that used to carry the sweet, earthy smell of fresh mushrooms now smelled of mud with a sour, rotten edge. The bottom rows of bags were soggy. Some had dark green patches spreading across the substrate, others had black spots and grey, fluffy growth. Several bags had mud inside the plastic. The upper rows, which the water never reached, still looked white and healthy, but clouds of tiny fruit flies were already circling them.

Auntie Boonma asked the question that many mushroom growers in Bang Len are asking right now: "Our whole farm is about growing a fungus. How do we know which mold is our mushroom and which mold is destroying it? And if we disinfect, won't we kill whatever mushrooms we have left?"

This article answers that question step by step. It rests on one rule that has no exceptions: we never fog disinfectant onto, or ozone-treat, mushroom blocks, fruiting bodies or spawn that are still alive. All of the disinfection work described here happens in grow houses, rooms and stores that have already been emptied. If you remember only one thing from this page, remember that.

Good Mold and Bad Mold: Telling Them Apart in a Grow House

The mushroom you grow is a fungus that you deliberately feed and protect inside a bag of substrate. Healthy mushroom mycelium is usually an even, bright white, spreads neatly through the whole block and smells like fresh mushrooms. Contaminating molds are other fungi that move in to compete for the same food, or that grow on the racks, walls and roof of the grow house. After a flood, contamination has every advantage: humidity is extremely high, air movement is poor, and the floodwater has carried in soil, rotting leaves and sewage.

Here are the signs growers in the Tha Chin basin typically see once the water drops:

• Green or dark green patches on the block. Growers usually just call this "green mold". It is one of the most common contaminations in blocks that have become too wet, and it spreads readily to neighbouring bags.
• Black spots, grey fluffy growth or orange-pink patches. These are other contaminating molds, not mushroom mycelium.
• Soggy bags with standing water inside, or a sour, rotten smell. Even if no mold is visible yet, this tells you the substrate is breaking down and bacteria are growing.
• Black staining on bamboo racks, wooden walls and thatch. This is mold growing on the structure itself. It becomes a reservoir of spores that will contaminate new blocks in the next cycle if it is left in place.

This is not a technical manual on mushroom cultivation. For diagnosing specific mushroom diseases or choosing new spawn, please talk to the Bang Len district agricultural extension office or another local agricultural agency. What a farm owner can do straight away, though, is sort the blocks decisively and get the grow houses genuinely clean before a new batch arrives.

Which Blocks Must Go and Which Might Be Kept

This is the most painful decision on any flooded mushroom farm, and also the most important. If it is made half-heartedly, contamination from the spoiled bags will spread through the whole house. Use these simple rules:

• Blocks that were submerged or soaked by floodwater: discard them all. Floodwater can carry germs from sewage and bacteria associated with leptospirosis. Mushrooms that grow from these blocks should not be sold or eaten.
• Blocks with green mold, black mold or a rotten smell: discard them. Bag them or close them up before you lift them, so you do not shake a cloud of spores through the house as you carry them out.
• Upper-row blocks that stayed dry, with white mycelium and no unusual smell: these may be moved to a dry area well away from the flooded grow house and watched closely. At the first sign of foreign mold, take the block out.
• Mushrooms that fruited during the flood or just after it, in a house that was flooded: do not sell them. A short-term loss is far better than a risk to your customers' health and to your farm's name.

Pile discarded blocks well away from the grow houses and the family home, never beside the grow-house door, because the pile itself becomes a source of spores and fruit flies. If your community has a collection point or local guidance for agricultural waste, follow it. Anyone carrying spoiled blocks should wear rubber gloves, boots and a mask, and wash their hands thoroughly every time they finish.

It also helps to keep a simple record: how many blocks were discarded from each house and roughly when they were made. That record will be useful when you plan how many new blocks to order and when.

The Damage Goes Beyond the Blocks: Health, Income and Reputation

• The health of the people on the farm. Carrying out spoiled blocks and shovelling mud exposes workers to huge numbers of mold spores. People with allergies or asthma may cough, sneeze or feel tight in the chest. Cuts and scratches on hands and feet that have been in floodwater can become infected, and wading in floodwater is linked to leptospirosis. Anyone who develops a high fever and aching calf muscles after working in floodwater should see a doctor and mention that they were in the water.
• Interrupted income. A mushroom farm runs on daily cash flow. Every day a grow house is not ready for new blocks is a day of income lost.
• Contamination carried into the next cycle. If green and black mold spores are still lodged in bamboo racks and floors, a new batch of blocks worth tens of thousands of baht can be contaminated within its first week.
• Reputation with traders and regular customers. Market traders in Bang Len and regular buyers remember which farm's mushrooms are fresh and clean. If mushrooms leave the farm smelling musty or spoiling quickly, trust disappears faster than the income does.
• The packing room and the family home. A packing room that was flooded needs to be as clean as a kitchen, because it handles food. And the family's raised wooden house is suffering from the same mold and musty smell as the grow houses.

Why the Usual Fixes Are Not Enough

• Pouring bleach everywhere. In a closed grow house the fumes are harsh on the eyes and lungs, and liquid bleach does not reach into the pores of bamboo, the layers of thatch or the gaps between rack joints, which is exactly where mold hides.
• Blasting everything with a high-pressure hose. It removes mud, but it also raises humidity again and scatters spores all over the house.
• Just opening the house to the wind. Airflow helps the house dry, but mold embedded in the structure does not disappear on its own.
• Rushing new blocks in to restart income. This is the most expensive mistake of all. The new blocks become fresh food for the contamination that is still in the house.
• Burning incense or using air freshener in the packing room. It only masks the smell for a while, and the scent can transfer onto the mushrooms being packed.

The Solution: Disinfecting and Ozone-Treating the Empty Grow House With World Health Disinfection

The World Health Disinfection (WHD) team approaches mushroom farms with a single principle: clean the environment, never the crop. Every step below begins only after all mushroom blocks, fruiting bodies and spawn have been removed from the area being treated.

1. Farm survey. We look at how high the water rose in each grow house, the packing room, the substrate store and the family home. We plan the order of work so that nothing affects the healthy blocks you have moved to a separate area.
2. Clean-up advice. Spoiled blocks and mud come out first. Floors and racks are washed, and rotten materials such as torn shade net or thatch panels that have broken down into mold are removed.
3. Disinfection fogging with Chemgene HLD4H. A ULV fogger produces a very fine mist that drifts into the gaps in bamboo racks, under the roof and into the corners of the house, as well as through the packing room and store. CHEMGENE HLD4H disinfectant has no harsh smell and is used according to its label instructions.
4. Ozone treatment of spaces that can be closed. For the packing room, storerooms and any grow house that can be sealed, a controlled dose of ozone helps destroy airborne mold spores and break down the smell of mud and rot.
5. Ventilation. The space is opened up until the ozone has fully broken down and the air is fresh, before anyone goes back in to work.
6. Re-check and planning for new blocks. We check smell, humidity and the old mold stains, and advise you to let the house rest and dry properly before new blocks arrive.

The rule with no exceptions: during disinfection fogging and ozone treatment there must be no mushroom blocks, fruiting mushrooms, spawn, plants, people or pets in the space. Ozone damages living cells, which is precisely why it works on mold, and it cannot tell the difference between the mold you want and the mold you do not. It is never used on blocks that are still producing. Any blocks you have kept must be stored in a separate area some distance away. Electrical equipment such as misting pumps and scales should be moved out or covered, and rubber items should be removed beforehand. The dose is controlled to suit the size of the space.

Every Zone on a Mushroom Farm, and the Right Approach for Each

• Fruiting houses (once emptied). Wash out the mud, fog the racks and floor thoroughly, consider ozone if the house can be closed up well, then let it rest and dry.
• Packing room and sorting area. Clean tables, baskets and scales, fog the surfaces, then ozone-treat the empty room to remove odors. Before packing mushrooms again, rinse food-contact surfaces with clean water as advised.
• Store for sawdust, rice bran and bags. Substrate materials that got wet should be thrown away, because damp sawdust and bran turn into mold farms almost immediately. Then fog and ozone-treat the empty store.
• Sterilising room and inoculation room (if you have them). Clean these with extra care, because they are the parts of the farm that must be cleanest of all. Remove all spawn before any work starts.
• The family home. Disinfection and residential ozone treatment deal with mold on wooden walls, mattresses and wardrobes, so the people who run the farm can actually rest.

Protecting the People Who Do the Clean-Up

On a family farm the clean-up crew is usually the family itself, plus a few neighbours or regular workers. The work is heavy and dirty, and it is easy to forget basic protection when everyone is tired and worried about money. A few habits make a real difference:

• Cover hands and feet. Wear rubber gloves and boots while carrying blocks and shovelling mud. Cover any cuts with waterproof dressings before starting.
• Wear a well-fitting mask. Moving moldy blocks releases large numbers of spores. A properly fitted mask is far better than nothing, especially for anyone with allergies or asthma.
• Keep children and elderly relatives away. They should not help carry spoiled blocks or play near the discard pile.
• Wash and change before going home. Wash hands and arms with soap, and change out of work clothes before entering the house, so spores and mud stay outside.
• Take breaks and drink clean water. Heat and humidity in a closed grow house are exhausting, and accidents happen when people are worn out.

Looking after the people matters as much as looking after the grow houses. A farm cannot restart if the people who run it are unwell.

Planning the Restart: A Simple Timeline for the Next Cycle

Every farm is different, and the right timing depends on how wet your grow houses still are. Many growers find it helpful to think in stages rather than dates:

1. Stage one, clear out. Remove every spoiled block, all wet substrate and all mud. Move healthy blocks to a separate dry area.
2. Stage two, wash and repair. Wash racks and floors, replace rotten bamboo, torn netting and broken thatch, and clear drains around the houses so water does not pool again.
3. Stage three, disinfect. Fog the empty houses, packing room and store, and ozone-treat the spaces that can be closed.
4. Stage four, rest and dry. Leave the houses open to air and sun until the floor is properly dry and there is no musty or chemical smell.
5. Stage five, restart small. Bring in a smaller batch of new blocks first and watch them closely. If they colonise and fruit normally, scale back up.

Restarting small costs a little time but protects the bigger investment. If contamination appears in the first batch, you will know before you have filled every rack.

10 Reasons Mushroom Farms in Bang Len Choose WHD

1. We understand that a mushroom farm is a fungus farm, so we never disinfect a space that still holds blocks or spawn.
2. Fine-mist disinfection fogging reaches the gaps in bamboo racks that a scrubbing brush cannot.
3. Chemgene HLD4H has no harsh smell, which suits a room where food is packed.
4. Ozone treatment of empty rooms helps reduce airborne spores and the smell of mud and rot.
5. Work is scheduled to fit the farm's plan for bringing in new blocks.
6. Ozone dose is controlled to the size of the space, with clear ventilation instructions.
7. Grow houses, packing room, store and family home can all be handled in one booking.
8. Practical advice on sorting spoiled blocks and protecting workers while they carry them out.
9. Mosquito spraying is available for farms with standing water around the houses.
10. Easy to reach by phone and LINE. Send photos of your grow houses for an initial assessment.

Before and After: Uncle Serm's Grow House

In the Customer's Words

"At first I was afraid that once they sprayed disinfectant, mushrooms would never grow here again. The team explained they would only treat the houses we had already emptied, and told us to move the blocks we kept over to the other side of the farm. After the work the mud smell was gone and we could use the packing room again. We let the houses dry as they suggested before bringing in new blocks."

— Auntie Boonma, grey oyster mushroom farm, Bang Len district (illustrative scenario)

Frequently Asked Questions

Q: Can I ozone-treat my mushroom blocks to kill the green mold?
A: No. Ozone does not choose which fungus to destroy, and mushroom mycelium is a living fungus too. Blocks with green mold should be discarded, and ozone is used only in spaces that are already empty.

Q: How long after disinfection can new blocks come in?
A: It depends on how damp the house is. Ventilate until there is no smell and the floor is genuinely dry, and follow the team's advice and the product label. Many growers choose to rest a house for several days before starting a new cycle.

Q: Can I sell mushrooms from upper-row blocks the water never reached?
A: If that grow house was flooded, it is safest to hold off selling until the blocks have been moved to a clean area and new flushes look completely normal. Your customers' safety comes first.

Q: Do bamboo racks with black stains have to be replaced?
A: If the bamboo is rotten, soft or deeply stained, replace it. If it is still sound, scrub it, dry it in the sun and fog it, and it can usually be used again.

Q: Does ozone work in an open shade-net grow house?
A: Ozone needs a space that can be closed to work properly. In very open houses the focus is on washing and fogging, while ozone suits the packing room, storerooms and the family home.

Q: Can you treat our house on the farm at the same time?
A: Yes. We can schedule it on the same day or the next. Everyone must leave the house during ozone treatment and return only after ventilation.

Q: Is the disinfectant safe around food?
A: Chemgene HLD4H is used according to its label. In the packing room, food-contact surfaces are rinsed with clean water before use, and no mushrooms are present during treatment.

Get Your Grow Houses Clean Before the Next Batch Arrives

Serving mushroom farms, other farms and homes in Bang Len, Kamphaeng Saen, Don Tum, Nakhon Chai Si and nearby areas of Nakhon Pathom.

View Disinfection Service – Click Here

Book Ozone Treatment – Click Here

Call 065-556-6294 · LINE @whd268 · Email worldhealthdisinfection@gmail.com

Related Pages and Sources

• Ozone treatment for odors and chemical residue
• Residential ozone disinfection
• CHEMGENE HLD4H spray disinfectant
• All articles
• External sources: WHO: Floods and health and Thailand Department of Disease Control

#MushroomFarmDisinfection #PostFloodDisinfection #OzoneTreatment #MoldRemoval #MustyOdorRemoval #Disinfectant #FarmFloodRecovery #HomeFloodRecovery

Keywords: disinfecting mushroom grow houses after a flood, mushroom farm flood recovery, green mold mushroom blocks, ozone treatment empty grow house, musty odor removal, Bang Len, Nakhon Pathom 2026