Round brown spots with yellow halos on lower leaves
Small spots with bright yellow halos on the lowest leaves climb the plant in wet, humid weather; spots grow and merge..
- Also called
- leaf spot
- brown spots yellow ring
- target spots
- septoria
- yellow leaf spot
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.
PossibleSeptoria leaf spot
Fix: Mainly outdoor and greenhouse. Strip infected lower leaves into a bag, keep foliage dry (water at the base), mulch to stop splash, open the lower canopy, clear debris; protectants only where registered.
Recovery: Spots stop climbing within 1-2 weeks.
How to confirm it
- Send a sample to a plant diagnostic lab. For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks.
- Magnifier check of leaf undersides and new growth. Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth.
Look for
Distinct roughly round tan-brown spots 2-6 mm with bright yellow halo, sometimes tiny black dots (fruiting bodies) in the centre..
The full guide: Septoria leaf spot (yellow leaf spot) in cannabis
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.
