Powdery Mildew, Botrytis & Root Rot
The three fungal/oomycete diseases that thrive on the humidity and dense canopies of late flower — the exact RH, temp, and VPD conditions that trigger them, and the environmental controls that shut them down.
Every disease in this lesson is triggered by conditions you control. Powdery mildew, Botrytis, and root rot don't appear randomly — they appear when RH runs too high, airflow stalls, canopies get too dense, or media stays too wet. That's good news: the same environmental setpoints that steer your crop also decide whether these pathogens can establish. Chemistry here is a supplement to environment, never a substitute.
| Disease | Signature | Trigger conditions | Threshold | Primary control |
|---|---|---|---|---|
| Powdery mildew | White powdery circular colonies on upper leaf; wipes off, returns | RH >55–60%, 20–26 °C, stagnant air, dense canopy; needs NO free water | Zero tolerance on flower | RH <55–60%, laminar airflow, defoliate interior; K-bicarb / sulfur; Bacillus |
| Botrytis / bud rot | Bud interior brown/mushy → gray fuzz; leaf near bud 'flags' | 15–20 °C, RH >60%, free water/condensation on tissue | Zero tolerance | Night RH ≤50%, leaf never below dew point, raise VPD in ripening; remove + bag |
| Fusarium / Pythium root rot | Wilt despite wet media; brown mushy 'rat-tail' roots; damping-off | Warm/saturated media, low dissolved O₂, warm reservoir | Act on first confirmation; rogue severely affected | Raise DO, cool reservoir <20 °C, dry-backs, Trichoderma |
The rest of this lesson is for members
Unlock every department, SOP, calculator, and setpoint table — plus Leaf, your AI consultant, and interactive diagnostics.
- All 11 departments
- Coco & rockwool tracks
- The full SOP library
- Leaf AI consultant