Small tan dead specks between veins on upper leaves
Appears late on leaves already showing netted interveinal yellowing..
- Also called
- tiny brown dots upper leaves
- pinpoint necrosis
- speckled top 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.
PossibleManganese deficiency
Fix: Correct high pH and alkalinity first. Supply about 0.3-0.8 mg/L Mn (manganese sulfate or chelate); avoid large iron chelate doses that compete with Mn.
Recovery: New upper leaves lose the netted pattern within 7-10 days.
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.
- Leaf tissue analysis. Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency.
Look for
Pinpoint tan spots scattered between veins of yellowing upper-middle leaves; nothing on the underside under a lens..
The full guide: Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance
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.
