Tell us where the problem shows up, then what it looks like. We’ll give you 2–4 possible causes with a simple check for each — never a certain diagnosis from a description alone.
Step 1 — Where’s the problem?
How it’s figured
Each symptom maps to the most common culprits from standard garden references (nutrient-deficiency guides, pest and disease manuals, and Extension plant-problem resources). These are the usual suspects, ordered sensibly — but a description alone can’t give a certain diagnosis. Your county Extension office can diagnose from photos or samples, and that’s the certain answer. A soil test is the certain answer for nutrition questions.