Mushrooms
Senior 2 · Agriculture
Mushrooms
Lesson 3 of 3
22 min
Let's begin
A youth cooperative in Huye fills 200 tubes in one morning. Six weeks later the first grey oyster mushrooms are packed for a hotel kitchen. Between those two days the growers do not water a field or weed a single row, but they must watch temperature, humidity, air and cleanliness every day.
This lesson follows a tube from spawning to harvest, explains the conditions that decide the yield, and shows how to recognise and prevent the common diseases and pests.
| Factor | Effect |
|---|---|
| Temperature | Too hot (above about 30 °C) slows growth and favours moulds; too cold delays fruiting. |
| Relative humidity | Too dry: caps crack and pins dry out. Water pouring onto caps: bacterial rot. |
| Ventilation (fresh air) | Carbon dioxide builds up in a closed room, producing long stalks and tiny caps. |
| Light | Dim indirect light is needed to form normal caps; direct sun dries and overheats the tubes. |
| Hygiene | Dirty rooms, tools and hands spread moulds, bacteria and insects. |
| Substrate and spawn quality | Decide how fast the mycelium colonises and how many flushes the tube gives. |
| Problem | Signs | Prevention and control |
|---|---|---|
| Green mould (Trichoderma) | Green patches in the tube; mycelium stops growing | Good pasteurisation and hygiene; remove infected tubes at once and destroy them far from the house |
| Other moulds (black, orange, pink) | Coloured, often powdery growth, sour smell | Correct moisture and heat treatment; discard infected tubes |
| Bacterial blotch (Pseudomonas) | Yellow-brown, slimy spots on caps | Mist the air, not the caps; improve ventilation; avoid standing water |
| Mushroom flies (sciarid and phorid) | Small flies; maggots tunnelling in stalks and caps | Fine mesh on windows and doors; sticky traps; remove spent substrate and rotting mushrooms |
| Mites | Tiny moving specks; damaged caps | Hygiene; clean shelves between crops |
Because mushrooms are eaten fresh and absorb chemicals easily, prevention through hygiene is far better than spraying.
Question: The cooperative's 200 tubes each contain 1 kg of dry substrate. Over all flushes they harvest fresh mushrooms equal to 60% of the dry substrate mass. Suppose each tube costs 600 Frw to make (substrate, spawn, bag, fuel) and the mushrooms sell at 2,500 Frw per kg. Find (a) the harvest, (b) the income, (c) the profit before labour.
(a) Dry substrate = 200 × 1 kg = 200 kg. Harvest = 60% × 200 = 0.6 × 200 = 120 kg.
(b) Income = 120 kg × 2,500 Frw/kg = 300,000 Frw.
(c) Cost = 200 × 600 = 120,000 Frw. Profit = 300,000 − 120,000 = 180,000 Frw, before paying for labour and the house. Losing even 20 tubes to green mould would cut the harvest by 12 kg (30,000 Frw), which is why hygiene pays.
Growers call the ratio of fresh mushrooms to dry substrate the biological efficiency: here 120 ÷ 200 × 100 = 60%.
Tip
Memory hook: the fruiting room needs "WATCH": Water in the air (humidity), Air (ventilation), Temperature, Cleanliness, Half-light.
Exam technique: link each disease to its cause. Green mould comes from poor pasteurisation and hygiene; bacterial blotch comes from wet caps and poor air.
What is a spawn run and when is it complete?
Solution: It is the incubation period during which the mycelium grows through the substrate in a dark, warm room. It is complete when the whole tube is white with mycelium.
Oyster mushrooms in a closed room have long thin stalks and very small caps. Explain and correct.
Solution: Carbon dioxide has built up because of poor ventilation. Open vents or windows (covered with mesh) to give fresh air.
Why should oyster mushrooms be harvested before the cap edges turn upwards?
Solution: After that stage the mushroom becomes tougher, loses quality and sheds large amounts of spores, which dirty the room and can irritate workers' lungs.
A grower gets 3.2 kg of fresh mushrooms from a tube holding 4 kg of dry substrate. Calculate the biological efficiency.
Solution: 3.2 ÷ 4 × 100 = 80%.
State two ways to prevent mushroom flies.
Solution: Any two: fine mesh on windows and doors; sticky traps; remove spent substrate and rotting mushrooms promptly; keep the house clean.
Summary
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
