# Differential diagnosis

> The method of listing every cause that could produce a symptom, then ruling causes out with cheap checks and tests until one or two remain.

- Canonical: https://genetixbay.com/knowledge/glossary/differential-diagnosis.html
- Also written: diagnostic differential, rule-out list
- Glossary category: Cultivation and training · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

A differential diagnosis is the clinician's way of thinking applied to plants: list all the causes that fit the symptom, then eliminate them in order of likelihood and cost of checking. Plant nutrition texts stress that visual symptoms alone are often ambiguous and need confirmation by analysis or by the plant's response to correction (Marschner 2012).

## In practice

GenetixBay's order is: where on the plant it started, the pattern, then [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) and watering, [pH](https://genetixbay.com/knowledge/glossary/ph.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), climate, light, pests and disease, and only then a nutrient. The diagnosis graph behind the symptom checker scores each cause this way and asks the question that best separates the leading candidates.

## Don't confuse with

- **A guess from one photo**: one answer with no ruled-out alternatives.
- **A tissue test**: one of the tests used within a differential, not the method itself.

## Related terms

[Chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Grow journal](https://genetixbay.com/knowledge/glossary/grow-journal.md), [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md)

## Read more

- [How to diagnose any cannabis plant problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md)
- [Cannabis lookalike problems: how to tell them apart](https://genetixbay.com/knowledge/diagnosis/lookalikes.md)
- [How to describe your plant's problem so it can be diagnosed](https://genetixbay.com/knowledge/diagnosis/how-to-describe-your-plants-problem.md)

## Sources

1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9