Yellow, curling, mottled leaves on my potted tomato plant. What is it?

by Mary B.
(Winterset, IA)

Q. How do I treat yellow, curling, mottled leaves on my potted tomato plant?

A. Yellowed leaves by themselves could indicate under-watering, over-watering, a nutrient deficiency, various wilts (such as fusarium wilt, verticillium wilt, or walnut wilt, infection from a pest such as aphids or white flies, or one of several fungi diseases.

But with the mottled foliage along with yellowed leaves, there's a good chance your plant has acquired either early blight or Septoria leaf spot.

Both are caused by fungi that over-winter in the soil.

Early blight causes leaves to yellow, curl, and develop dark spots with concentric rings. Fruit can also develop spots.

Septoria leaf spot shows first on lower leaves with yellowing, curling, and dark spots. Septoria begins on lower leaves and works its way up the plant. Fruit is not affected.

Both early blight and Septoria leaf spot can be treated with copper spray, a biofungicide (like Serenade) or a fungicide (like Mancozeb or Fungonil).

But prevention is the most effective way to offset tomato blights of any kind, including early blight and Septoria leaf spot. Be sure to fill containers with sterile potting soil at the beginning of the season. (Fungus for both early blight and Septoria lives in the soil.) Plant blight-resistant varieties. Mulch plants to prevent water from splashing up on leaves and spreading fungus. Avoid overhead watering. Rather, water with a drip hose at the soil line.

Good Luck and Happy Gardening!
Your friends at Tomato Dirt