Black Spots on Tomato Leaves

Picture of tomato plant leaves with Septoria leaf spot disease.

Hey Dan, I was wondering what you think of the small black dots on my tomato plants. Thanks for your input. They are on several leaves on one plant.

- Gary B.

This is Septoria leaf spot, a common fungal disease of tomatoes.

Remove diseased leaves. If caught early, the lower infected leaves can be removed, bagged and disposed of. However, removing leaves above where fruit has formed will weaken the plant and expose fruit to sunscald. Do not compost diseased plants.

Improve air circulation around the plants. Make sure plants are spaced properly.

Mulch around the base of the plants. Mulching will reduce splashing soil, which may contain fungal spores associated with debris. Apply mulch after the soil has warmed.

Do not use overhead watering. Overhead watering facilitates infection and spreads the disease. Use a soaker hose at the base of the plant to keep the foliage dry. Water early in the day.

Use crop rotation. Next year do not plant tomatoes back in the same location where diseased tomatoes grew. Wait 1–2 years before replanting tomatoes in these areas.

Use fungicidal sprays. Fungicides will not cure infected leaves, but they will protect new leaves from becoming infected. Apply at 7 to 10 day intervals throughout the season. Apply chlorothalonil, maneb, macozeb, or a copper-based fungicide, such as copper hydroxide, copper sulfate, or copper oxychloride sulfate. Follow harvest restrictions listed on the pesticide label.

Dan Gill
Consumer Horticulture Specialist

9/12/2015 3:23:26 AM
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