🍄 Pests and Diseases

This module is about the organisms that damage your crop. Before you learn any one of them, you need to understand the principle that governs all of them, and you need to know exactly how strong the evidence behind this module is. Take the second point first, because it is unusual for a course to tell you.

The honest position on the evidence. This course's reference material states plainly that its pest and disease evidence base is entirely non-African. Every named organism and every number in this module comes from one of three places: United States commercial and extension mushroom literature, general mycological literature, or a single qualitative severity statement in a Botswana government production guide. There is no African incidence survey for green mould. None for cobweb disease. None for the bubble diseases. None for bacterial blotch. None for sciarid flies, phorid flies or mites. Nobody in the sources used here has measured how common any of these problems actually are on African farms.

What does that mean for you? It means the biology is trustworthy and the frequency is not. A fungus that outcompetes mycelium for space and food does that in Nairobi exactly as it does in Pennsylvania - the mechanism does not change with the continent. But whether green mould or flies will be your main problem, and how often, is something you will have to find out from your own records. This course will not pretend to know. When someone tells you confidently that a particular pest is "the big one in Africa", ask them where they measured it.

Now the governing principle. Every pest and disease in this module is, at root, a contamination and hygiene problem, not a chemical problem. Remember what you learned about contamination in earlier modules: it is a race between organisms. Your substrate is a rich food source that any fungus or bacterium can use. You are trying to give your chosen mycelium a head start over every competitor already present in the straw, the sawdust and the air of your room.

That framing changes what you do. If you think of green mould as a disease, you look for a spray. If you think of it as a competitor that got into your bag, you look at how it got in - your pasteurisation, your spawn, your hands, your tools, the air in your room. The second question has an answer you can act on. The first mostly does not, because for most of these problems there is no practical curative treatment once the organism is established inside a bag.

So the highest-leverage lesson in this whole module is this: sanitation, correct moisture, correct temperature and correct spawn and substrate handling prevent almost everything on this list, far more reliably and far more cheaply than any treatment applied afterwards. Everything you already learned about pasteurisation, spawn checking, moisture targets and clean working is your pest control programme. You have been doing pest control since module one without calling it that.

What a preventive routine actually contains, drawn from the sourced control principles across this module:

1. Treat the substrate properly. Correct pasteurisation of bulk substrate, correct sterilisation of grain spawn. Under-treated substrate is the most common single route in.
2. Check spawn before you commit substrate to it. Green, black, pink or orange patches, sour or ammonia smells, slimy grain - reject it. Bad spawn carries the contaminant straight into the middle of your batch.
3. Work clean. Wash hands. Wash and disinfect surfaces. The Botswana guide names washing with water and disinfecting with formalin, bleach or steam for growing-house walls.
4. Exclude flies. Fine insect mesh over every vent and opening. This is core infrastructure, not an optional extra, and the next-to-last lesson explains why.
5. Remove and dispose of affected material fast, and far away. Not composted next to the growing rooms. Ideally the same day you spot it.
6. Keep the surroundings clean. Piled organic waste outside the house breeds flies independently of your crop.
7. Write down what you saw. Your own observation log is the only source of information about what is actually common on your farm, because as this lesson opened by saying, no one else has measured it.

One last framing point. Chemical control comes last in this module, and it is governed entirely by your national regulator. It is last because it is genuinely the least useful lever available to a small grower, not because it is being saved for the end as a reward.

Of everything named in the sources gathered for this course, green mould is the single most economically damaging contaminant. It is caused by fungi of the genus Trichoderma. The Botswana production guide describes it as fast-growing and capable of causing 100 percent losses in an affected batch.

Read that severity figure carefully, because it matters how you use it. It is a general statement of severity from that guide - a warning that an affected batch can be a total loss - not a measured incidence rate telling you how often it happens. No African Trichoderma strain identification, prevalence survey or loss-rate study was retrieved for this course. So you should treat green mould as capable of destroying a batch entirely, and you should not carry around any figure claiming to know how many of your batches it will affect.

How to identify it. Trichoderma starts as a dense white mycelial growth on the substrate surface. That is the difficult stage, because at that point it looks broadly like the mycelium you want. Then it sporulates and turns green - a distinct, often vivid green that spreads fast across the surface. By the time it is green it has already been growing for some days and has already produced spores.

That sequence explains why your daily visual check matters so much. If you look at your bags only once a week, you will meet green mould at the green stage, when it is sporulating into the air of your room. If you look every day and know what your own healthy mycelium looks like, you have a chance of catching an odd, unusually dense white patch earlier and getting that bag out before it sporulates.

Why it wins. Trichoderma is fast-growing. It competes with your crop mycelium for the same space and the same nutrients in the same substrate. This is the race framing again, in its purest form. Nothing about green mould is mysterious - it is simply another organism that eats what your mushroom eats and, given an opening, gets there first.

Control is entirely preventive. That is the reference's own wording and it is worth stating flatly: there is no practical curative treatment once Trichoderma has established inside a bag. You cannot spray it out. You cannot cut it out, because the visible green surface patch is the fruiting of a network that has already spread through material you cannot see. Anyone who tells you they saved a green-moulded bag saved a bag that was going to be fine anyway, or lost the rest of their room to it later.

So where does it come in? Three routes, and almost every case traces to one of them.

1. Inadequate pasteurisation or sterilisation. The substrate went into the bag still carrying viable competitor organisms. Check your method, your temperature, your duration, and whether your timer started before or after the vessel actually reached temperature.
2. Contaminated spawn. The contaminant arrived in the middle of the substrate, in the material you deliberately distributed evenly throughout it. This is why the five-minute spawn check before you commit a batch is one of the highest-value habits in the course.
3. Poor hygiene. Hands, tools, work surfaces, the air of a dirty room, or spores blowing in from an affected bag or a waste pile nearby.

What to do when you find it. Remove the bag. Do not open it in the growing room - carry it out sealed if you can. Dispose of it well away from the active growing house, and specifically not on a compost heap sitting next to your rooms, which is simply a spore factory positioned upwind of your crop. Then wash and disinfect the shelf and surrounding surfaces before putting anything else there.

Then investigate. One green bag in a batch of fifty is bad luck or one handling slip. Green bags appearing in every batch is a system fault, and you find it by laying your last several batch records side by side and looking for what the affected batches share: the same spawn delivery, the same pasteurisation day, the same person handling, the same room. Without those records you will guess, and growers usually guess the most expensive cause rather than the true one.

One cross-link worth holding on to. The next-to-last lesson in this module covers sciarid flies, which the research literature documents as benefiting from and spreading green mould in commercial cultivation. If you have a green mould problem and a fly problem, you do not have two problems. You have one problem with two visible symptoms, and screening your vents is part of your mould control.

Three more fungal diseases appear in the sources for this course. All three are worth knowing so you can recognise what you are looking at, and all three come with a bigger evidence warning than green mould does. Read the warnings as carefully as the descriptions.

Cobweb disease first. It is caused by species of Cladobotryum in the general mycological literature. What you see is a fast-spreading, grey, cobweb-like mycelial growth over the substrate or casing surface. The word cobweb is a good description: it is wispy and loose, quite unlike the dense mat of Trichoderma, and quite unlike the fine bright white of healthy mushroom mycelium. Colour and texture together are your identification - grey and wispy rather than green and dense, or white and firm.

No African-specific source with numeric detail on cobweb disease incidence or control in African mushroom operations was retrieved for this course. So there is no incidence figure to give you, no loss percentage, and no control-trial result. What can be taught safely, and is taught here, is that the same preventive principles apply as for green mould: sanitation, prompt removal of affected material, and avoiding excess surface moisture. That last point is worth a moment. A wet surface is a hospitable surface for a competing fungus. The mushroom you want is fed from inside the substrate; the competitors are often fed from the surface, which is exactly where standing water collects if you mist carelessly.

Now the two bubble diseases, which come with a species warning as well as an evidence warning. Dry bubble is caused by Verticillium and Lecanicillium species; wet bubble by Mycogone species. Penn State Extension describes these, in its own words, as by far the most common fungal disease among commercially cultivated white button mushrooms. What they produce is unmistakable once you have seen it: instead of a normal cap and stem, the crop forms a globe-like, undifferentiated mass of tissue. The mushroom shape simply fails to develop.

The warnings, both of which you must hold at once. First, this is button mushroom disease literature, from a United States extension source. Button mushroom, Agaricus bisporus, is the crop it was described on. It is not an African finding. Second, this course's reference material is explicit that almost all detailed Agaricus disease and production literature it retrieved is non-African - and beyond the qualitative severity statement above, no numeric incidence, loss or control-threshold figure was captured from the source at all. So there is no percentage to give you here either.

What should you do with a disease description that carries this much uncertainty? Not ignore it, and not overstate it. The useful position is this: know what the symptom looks like so you can recognise it, know which crop it was documented on, and understand that if you are growing oyster mushroom - which this course recommends as the lead crop for most African growers - you are looking at a disease described on a different species in a different climate under a different production system. That is not a reason to assume you are safe. It is a reason to record what you actually see rather than to expect what a textbook from elsewhere predicts.

That brings us to the practical response that covers all three diseases in this lesson, and it is deliberately the same response.

• Look at your crop often enough to notice a change. Grey wisps, a globe of undifferentiated tissue, or anything else that is not the shape and colour you expect.
• Remove affected material promptly and dispose of it away from the growing house, exactly as for green mould.
• Do not let surface moisture sit. Mist the floor and walls rather than the crop, ventilate so that surfaces dry between mistings, and avoid leaving standing water on caps.
• Wash and disinfect surfaces, tools and hands. The same regime that keeps green mould out keeps these out.
• Write down what you saw, on what date, in which room, on which batch, and what it looked like. Draw it if that helps. Over a year that log becomes your own disease reference for your own farm.

One honest closing note. It is tempting, when a course cannot give you numbers, to skip the topic. This module does not skip it, because a grower who recognises cobweb disease and knows it needs immediate removal is materially better off than one who sees grey fluff and hopes it is nothing. Knowing what something is, and knowing that nobody has counted how often it happens where you live, is a perfectly honest and perfectly workable position for a working grower.

Bacterial blotch is the disease with the most complete numeric detail in this course's sources, which makes it worth studying closely - and it is also the disease most directly caused by something you do yourself, which makes it worth studying twice.

The organism. Bacterial blotch is caused by Pseudomonas fluorescens biotype G, historically referred to as Pseudomonas tolaasii. It is a bacterium, not a fungus, which is why it behaves differently from everything else in this module. It does not compete with your mycelium for substrate. It attacks the mushroom itself, after the mushroom has formed.

The symptoms. Fruiting bodies become discoloured and slimy, and the caps show water-soaked blotches. A crop with blotch is a crop you cannot sell. The mushrooms are still there, they are just unsellable - which in some ways is worse than losing a bag to green mould, because you have carried all the cost of the cycle right through to harvest before the loss appears.

Now the precipitating condition, and this is the sentence to remember from this whole lesson. Blotch develops when mushroom caps stay wet for four to six hours or longer after water is applied. The source is specific about the mechanism: condensation forms on the cap surface when the surrounding air is saturated and warmer than the cap. Note carefully that the trigger is moisture sitting on the cap, not humidity in the air by itself. High humidity is a condition your crop needs - the sourced fruiting target is a minimum of 85 percent relative humidity, and the Nigerian trial ran at 92 plus or minus 2 percent. High humidity is not the problem. Free water lying on the cap for hours is the problem.

This is exactly why the sourced humidity method says to mist the floor and walls of the fruiting room rather than spraying directly onto the mushrooms in a way that leaves standing water on the caps. You are trying to put water into the air, not onto the crop. A grower who sprays the mushrooms directly because it feels like it is doing more is manufacturing blotch conditions with their own hands.

The second sourced precondition takes you back to substrate preparation. Compost or substrate with a moisture content below 62 percent at the point of spawning is named as predisposing the crop to blotch. That is a direct link between a decision you made weeks earlier and a disease that appears at harvest. It is also one more reason to hit the sourced substrate moisture targets - 70 percent in the Botswana preparation method, 60 to 75 percent in the MushWorld handbook, 65 to 70 percent in both the Ethiopian and Nigerian trials - rather than run a batch deliberately dry because dry feels safer.

Control, then, is about water management, and it has three parts.

1. Keep caps dry. Do not spray water directly onto the crop. Mist surfaces instead.
2. Ventilate. Airflow across the crop dries cap surfaces and prevents the condensation the source describes. This is the same fresh-air exchange you already need for good cap formation, doing a second job.
3. Hit your substrate moisture target at spawning. Below 62 percent is named as a predisposing condition.

Now the chemical measure, and read this part carefully. The source also names sodium hypochlorite at 150 parts per million of chlorine added to irrigation water as a measure used in the United States commercial industry it describes. That figure is included here for one reason only: to show you how such a control is specified in a country that has approved it. It is not your rule. It is a United States commercial industry figure, not an African-regulator-approved figure.

What that means in practice is a rule you must apply to every chemical mentioned anywhere in this course. Before you use any chemical treatment on mushrooms intended for sale, you must check what your own country's food-safety authority or agricultural-chemicals regulator permits, and at what concentration. That is the kind of authority to ask: a national food-safety body or plant-protection and agricultural-chemicals authority. Do not treat a number from another country's industry as your permission. And note the trap explained further in the last lesson of this module: a product approved for use on vegetables generally does not automatically extend to mushrooms.

Finally, the evidence caveat, which by now you will expect. No African-specific bacterial blotch incidence or trial data was retrieved for this course. The mechanism is sound and well described. How often it will affect you is something your own records will tell you and nothing else will.

Insects are the other half of this module, and they are the half most small growers underestimate, because a fly seems like a nuisance rather than a threat. It is a threat, and the reason is not the one most people expect.

The two flies named in the sources are sciarid flies, of the genus Lycoriella, and phorid flies, of the family Phoridae. Penn State Extension describes sciarid flies as the most devastating insect in the Pennsylvania mushroom industry since 1979, and phorid flies as more numerous than sciarids but causing less damage. Both of those statements, and the ranking between the two, come from a United States commercial industry context. No African prevalence, loss or control-trial data for either fly was retrieved for this course. So take from that source what it can honestly give you - that sciarids do real, serious damage in a large commercial industry that studied them - and not a claim about which fly matters most on your farm.

The first way flies damage a crop is direct. Sciarid and phorid fly larvae feed on and physically damage mycelium and developing mushrooms. Larvae in your substrate are eating the organism you spent weeks growing.

The second way is the important one, and it is the reason this lesson exists in a module mostly about fungi. Flies are implicated in the literature as vectors that carry mould spores - including Trichoderma - from bag to bag, and from contaminated waste back into a clean growing room. The mushroom sciarid fly has specifically been documented in the research literature as benefiting from, and spreading, green mould disease in commercial cultivation. The fly does well where the mould is, and moves the mould around.

Sit with what that means. Fly control and green-mould control are the same job, not two separate jobs. A grower who has done everything right on pasteurisation and spawn hygiene, and who has open vents, has left a door open through which the contaminant walks - or flies - straight back in. And a grower who removes a green-moulded bag but leaves it sitting in a heap twenty paces away has built a station where flies breed, pick up spores, and carry them home.

Mites are the third pest. They are named across the general pest literature as a contaminant of grain spawn and substrate, feeding on mycelium and spreading contamination between bags on their bodies - the same vector role the flies play, on a smaller scale. No African mite prevalence, species identification or control-trial data was retrieved, and no numeric loss or threshold figure from any source could be confirmed well enough to teach as fact. So there is no mite threshold number in this course. What there is, is a control approach identical to the flies: clean spawn sourcing, sealed storage of unused grain and substrate, and prompt disposal of any visibly infested material.

Now the practical programme. Every item below is a sourced control principle, and every one of them is low cost.

1. Fine insect mesh over all vents and openings. This is the single most important physical measure, because it addresses both direct larval damage and spore vectoring at once. Screen every vent, window and gap. A screened room with one unscreened gap is an unscreened room.
2. Sticky traps to monitor fly pressure. Note the word monitor. Traps are not primarily a control method at small scale - they are a measuring instrument. Hang them, count them weekly, write the count down. A rising count tells you something has changed before your crop tells you.
3. Strict removal of spent substrate and any contaminated bags well away from the active growing room, ideally the same day they are identified. Same day. Not at the end of the week.
4. Keep the area around the growing house free of piled organic waste. This is the step most often skipped, and it is the one that matters most outside the walls. Waste piles breed flies independently of your crop - they do not need your mushrooms to build a population that then finds them.

A note on cost. Insect mesh over the vents of a small growing house is one of the cheapest interventions in this course, and it protects against a pest that damages the crop directly and a disease that can take a whole batch. Screening should be near the front of the queue, ahead of almost any monitoring equipment.

And a note on habit. Flies are a continuous pressure, not an event. There is no day on which you have finished controlling flies. That is why this belongs in a written weekly routine rather than in your memory, and it is what the capstone of this module asks you to build.

This module ends where a lot of growers want it to begin: with chemicals. It is last for two reasons. It is genuinely the least useful lever available to a small grower, and it is the one area where a wrong number in a course could poison a customer.

Start with the position this course takes, stated plainly. Everything about chemical pesticide and fungicide use on a food crop is decided by a national authority and differs by country. This course states principles and names the kind of authority to ask. It states no permitted active ingredient, no dose and no withholding period, because those differ by country and because an incorrect number here would contaminate your crop and could poison the person who eats it.

What the sources actually contain is worth knowing. Exactly one specific chemical control figure with a numeric dose appears anywhere in this course's reference material: the 150 parts per million chlorine irrigation-water treatment for bacterial blotch, from a United States commercial context, which you met in lesson four. That figure is explicitly not carried forward as an African standard. Beyond it, no fungicide, insecticide or sanitiser active ingredient, dose, or pre-harvest interval approved for use on a food-crop mushroom in any named African country was retrieved. None. That is not an oversight to be filled in by guesswork - it is correctly left empty by design.

So what do you actually do? You ask. The kind of authority you are looking for is your own country's agricultural-chemicals regulator or plant-protection authority, and for anything touching a product you sell to eat, your national food-safety authority. Many countries have a pesticide registration board or a plant health directorate inside the ministry of agriculture. Your nearest extension office will know its name, and so will the research institute you were told to approach for spawn.

The question to ask is narrow, and asking it narrowly is what gets a useful answer. Ask: is this specific product registered for use on mushrooms as a food crop in this country, at what concentration, and with what interval between application and harvest?

There is a trap inside that question that you must understand. A product's approval for use on vegetables generally does not automatically extend to mushrooms. Mushrooms are not vegetables. They are a different kind of organism entirely - and a fungicide, by definition, is designed to kill fungi, which is what your entire crop is. Applying a general-purpose fungicide to a mushroom crop is not a cautious act. It is applying a substance designed to kill the exact organism you are growing.

Then there is residue discipline. Any chemical used anywhere in your growing cycle - for pasteurisation, for pest control, for cleaning surfaces - that was not approved for use on a food crop by your own national regulator is a food-safety risk to your buyer, not merely a compliance risk to you. That includes the disinfectants you use on walls and shelves, if they can reach the crop or the containers it goes into. Ask about them too.

Now the part that will actually improve your farm, which is not chemical at all.

This module has told you repeatedly that the African incidence data does not exist. That gap is not going to close because you wish it would. What can close it, for your own operation, is a written log. Record, every time you see something: the date, the batch number, the room, what you saw, what you think it was, what you did, and what happened afterwards. Draw it if words fail you.

What that log gives you after a year is genuinely yours. You will know whether green mould is your problem or flies are, which season is worst, and whether the trouble follows a particular spawn supplier, substrate source, or a week when you were rushed. None of that is in any book, because nobody has written the book for your farm.

And here is the discipline that makes the log work: change one thing at a time. If you screen your vents, switch spawn suppliers and change your misting method in the same month, and your losses fall, you have three explanations and no way to choose between them. Change one thing, date it in your log, and give it enough batches to show a difference.

One closing rule that belongs in this module and in your business. Never sell a batch that shows contamination mixed in with clean product, even if only part of the harvest looks affected. Your customer cannot see the mould that was growing on the bag next door. A single reported illness or one visibly mouldy punnet damages a small grower's reputation far more than the value of the product you would have thrown away.