根腐れは、病原性水生カビ（主にPythiumやPhytophthora属）が引き起こす植物病害で、水浸しや酸素不足の環境で根を侵食・分解します。罹患した根は茶色または黒色になりドロドロした状態になり、水分と養分を吸収する能力を失います。
主なポイント
- Primary pathogens: Pythium and Phytophthora water moulds, often pre-existing in water supplies
- Triggered by: insufficient dissolved oxygen, warm reservoir temperatures, and stagnant water
- Symptoms: brown/black slimy roots, wilting despite adequate water, yellowing leaves
- Prevention: maintain dissolved oxygen with air stones, keep reservoir below 20°C (68°F)
- Treatment: beneficial bacteria (Bacillus subtilis, Trichoderma) can suppress Pythium
- Hydrogen peroxide (3 mL of 3% per litre) can sterilise severely infected reservoirs