Bronzed, rusty-looking leaf surfaces
Bronzing spreads up from lower leaves (russet mites) or from the tips (broad mites); leaf edges may curl up..
- Also called
- bronzing
- leaves look bronze
- rusty leaves
- leaves turning copper
- russet 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.
PossibleHemp russet mites
Fix: Confirm at 30-60x (they look like moving dust). Remove badly infested plants; release predatory mites preventively; quarantine clones; leave a plant-free gap between cycles.
Recovery: Bronzing stops climbing and no live mites at 30-60x in 2 weeks.
How to confirm it
- 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.
PossibleTwospotted spider mites
Fix: Act now: they breed fastest hot and dry. Remove the worst leaves into a sealed bag, cool the room and raise RH a little (in veg), release predatory mites (Phytoseiulus persimilis for hot spots, Neoseiulus californicus as a preventive) before numbers explode. Soaps or horticultural oils only in veg, never on buds. Quarantine new clones.
Recovery: No new stippling on new leaves and no live mites at 10-20x after 7-14 days.
How to confirm it
- 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.
- Tap a branch over white paper. Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier.
Less likelyBroad mites
Fix: Confirm at 30-60x. Remove and bag heavily infested plants; mothers and clones are the usual source. Release predatory mites (e.g. Neoseiulus californicus or Amblyseius swirskii) on the rest, keep tools and clothes clean, quarantine new stock. In flower, removal is usually the only clean option.
Recovery: New growth expands normally (not glossy or twisted) within 10-14 days.
How to confirm it
- 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.
- Watch new growth for 5-10 days after one change. Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days.
Less likelyIron and manganese excess at very low pH
Fix: Raise root-zone pH above ~5.5 (soilless) or 6.0 (soil); below about 5.3, Fe and Mn become very soluble. Cannabis Fe toxicity itself is not characterised.
Recovery: No new speckling on leaves that develop after pH correction.
How to confirm it
- Measure input pH and root-zone (runoff or reservoir) pH. Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend.
- 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
Dull bronze sheen on upper leaf surfaces with edges curling up; take a 30-60x photo..
The full guide: Broad mites on cannabis: life table, spread and control (plus russet mite summary)
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.
