Symptom differential
Necrotic Spots & Lesions
Dead spots can come from pathogens, pests, droplets, sprays, nutrient-related tissue failure, physical injury, or environmental damage. Lesion shape alone is rarely enough to identify cause.
Pattern questions
- Are spots bounded by veins or randomly distributed?
- Do lesions expand over time?
- Are there halos, concentric zones, fungal growth, frass, or insects?
- Do spots align with spray droplets or wetting patterns?
Plausible cause categories
- Fungal or bacterial disease
- Pest feeding
- Spray or droplet injury
- Nutrient or root-zone disorder
- Physical abrasion
- Light or heat injury
Discriminating checks
- Use magnification
- Track lesion expansion
- Review spray and wetting history
- Compare upper and lower leaf surfaces
- Submit samples for laboratory diagnosis when disease is plausible and consequential
Red flags
- Rapidly expanding lesions
- Stem or petiole involvement
- Sporulation
- Similar lesions spreading between nearby plants
Visual study guide
- Spot morphology vocabulary
- Expanding-versus-static lesion timeline
- Spray-droplet comparison
- Pest-sign overlay