Must-have
Powdery mildew
White powdery patches; improve airflow, avoid crowding, remove infected leaves, and use labeled organic fungicides when appropriate.
Plant diseases
The next visual library: fungal, bacterial, viral, and physiological problems with lookalikes and nonchemical prevention.
Must-have
Rust diseases
Orange or brown pustules; remove infected foliage, avoid overhead watering, and select resistant varieties.
Must-have
Leaf spots
Brown, tan, black, or yellow-ringed spots; improve sanitation and reduce leaf wetness.
Should-have
Root rot
Wilting in wet soil; check roots, improve drainage, repot, and water less.
Should-have
Damping off
Seedlings collapse; use clean trays, airflow, and careful moisture.
Should-have
Viral symptoms
Mosaic, rings, distortion; isolate and discard confirmed infected plants.