Tomato leaves have white spots
The upper leaves of a fast growing tomato plant has white spots in the top and underside of the leaf. I'm worried that it will spread. The tomato is potted and on a sunny south facing balcony. Is there something I can do to correct this? Pic attached.
Certified GKH Gardening Expert
This is the common first signs of Septoria leaf spot.
The leaf spots of septoria begin as small yellow specks, which later enlarge, becoming brown with a yellow border. They can be either circular or irregular in shape, and often have a black dot in the center. You will see them scattered all over the older leaves of infected tomato plants. If you feel this is the problem, apply copper dust or a liquid copper spray fungicide every 7 to 10 days after discovering the disease until 3 to 4 weeks before harvesting.