# Dark brown lesions on sugar leaves in flower: likely causes and fixes

> Dark brown lesions on sugar leaves in flower on cannabis is most often Potassium deficiency. How to tell them apart, the fix for each and what recovery looks like.

Also called: sugar leaves turning brown, brown spots on bud leaves, dark sugar leaf tips.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=dark-lesions-sugar-leaves

## Likely causes, most likely first

### Potassium deficiency (Possible)

- Kind: Nutrient; urgency: Deal with it this week
- Fix: Check runoff EC first: salt burn looks the same. If K is genuinely short, feed about 175-250 mg/L K (potassium sulfate, potassium nitrate or MKP) at a normal EC. A flowering DWC trial saw no yield response anywhere from 60 to 340 mg/L, so more is not better. Cut heavy Cal-Mag or sodium-rich water that competes with K.
- Recovery: Margin scorch stops advancing up the plant within 7 days; new leaves open with clean margins.
- Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed.
- Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium.
- Confirm: 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.
- Confirm: 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.
- Article: [Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance](https://genetixbay.com/knowledge/nutrients/potassium.md)

## Note

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.