Deficiency vs. Pest vs. Abiotic — The Master Diagnostic Table
The decision framework that separates a nutrient problem from a pest from an environmental one — firm-vs-limp, position, and the confirm step — capped by the full symptom→cause→confirm→fix table behind the diagnostics engine.
A yellow, curling, or spotted leaf can be a nutrient deficiency, a pest, or an abiotic (environmental) stress — and they routinely masquerade as each other. The discipline is to never fix on appearance alone: every diagnosis has a confirm step that distinguishes look-alikes before you act. Dose a phantom deficiency and you add salt stress; spray for a pest that's actually light burn and you've wasted product and stressed the crop.
1) Where is it? Lower/old = mobile nutrient or spider/russet mite or overwatering; new/top = immobile nutrient, broad mite, thrips, or light burn. 2) Firm or limp? Firm/full droop = overwatering; limp/dry = underwatering; firm + bleached under the lights = light burn (limp yellow = N deficiency). 3) Does it correct? A 'deficiency' that won't respond to a correct pH/EC fix is a pest or a root problem — pull the roots.
The rest of this lesson is for members
Unlock every department, SOP, calculator, and setpoint table — plus Leaf, your AI consultant, and interactive diagnostics.
- All 11 departments
- Coco & rockwool tracks
- The full SOP library
- Leaf AI consultant