Dark, water-soaked lesions on leaves or stems
Translucent, dark, wet-looking areas that enlarge and turn brown; common in humid, crowded canopies..
- Also called
- wet looking spots
- greasy spots
- dark soggy patches
- water soaked leaves
Likely causes, most likely first
Ranked for this sign on its own. Your stage, medium and readings change the order, so run the checker for your plant.
PossibleBotrytis bud rot (grey mould)
Fix: Act now. Bag infected buds before cutting them out, 3-5 cm (1-2 in) past visible rot, and clean tools; never shake them. Drop RH to about 40-50% in late flower, control the lights-off dew point, move air through dense colas. There is no cure in flower; consider harvesting early if it keeps spreading.
Recovery: No new rot on weekly cola checks for 2 weeks.
How to confirm it
- Open the densest colas. In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it.
- Check temperature and RH at canopy height with a calibrated sensor. Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point.
PossibleHumidity too high / VPD too low
Fix: Target about 55-70% RH in veg, 50-60% early flower, 40-50% late flower (leaf VPD 1.0-1.5 kPa in flower). Dehumidify, raise exhaust, keep air moving under the canopy and watch the lights-off spike (dew point). High RH in flower raised bud-rot risk and in one study delayed flowering and lowered cannabinoids.
Recovery: RH holds in band through lights-off for 3+ days; no new mould signs.
How to confirm it
- Check temperature and RH at canopy height with a calibrated sensor. Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point.
Look for
Glassy dark patches with a soft edge, sometimes with grey fuzz in humid conditions..
The full guide: Spots, brown patches and dead edges on cannabis leaves: the master decision tree
Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth.
