Diagnosing Brown Blotches on Greenhouse Tomatoes: Not Mosaic Virus

Ruling Out Mosaic

Tobacco mosaic virus causes yellow-green mottling, leaf curl, blisters—not brown blotches. Your symptoms suggest Septoria leaf spot or early blight (Alternaria solani), which produce discrete brown lesions, sometimes with halos.

Nutrient Check

Phosphorus, manganese, or calcium deficiency can cause browning. In peat-based pots, nutrients exhaust in ~4 weeks. Feed with balanced fertilizer.

Next Steps

Email close-up photos. Confirm if seedlings or purchased plants. Overwintered geraniums/fuchsias are unrelated hosts—unlikely common pathogen.