Remedies for a Leaf Spot on Tomatoes

Limiting Moisture

• Gardeners can't control the rain but they can control how they apply water to the tomatoes in the garden. Use a soaker hose or drip irrigation system to provide water only to the ground, not on the plant leaves. Water only in the morning so daytime sunshine evaporates any excess water on the plants. Mulching around the base of the plants prevents rain from splashing soil and moisture onto the plants.

Plant Selection

• Plant only tomatoes with resistance to early blight and septoria leaf spot. Plant breeders have developed these varieties to have at least some level of resistance and may be the best option if leaf spot has been a problem in your garden in the past. If growing tomatoes from seed, use only fungicide-treated seeds. Following the other preventive steps helps even resistant varieties avoid leaf spot.

Crop Rotation

• The fungus associated with the diseases that cause leaf spot lives in the soil. Planting tomatoes in different parts of the garden each year limits the effect of the soilborne fungus. Ideally, plant tomatoes in the same spot within the garden every four years. Additionally, space tomatoes far enough apart so natural air circulation can dry the foliage after a rain.

Chemical Treatment

• Applications of a fungicide containing chlorothalomin, maneb or benomyl reduces or eliminates the leaf spots. Each product has its own application ratios and procedures, so read and follow manufacturer's instructions. Most treatment plans call for fungicide treatments about once per week unless extreme wet conditions indicate more frequent use.