Cures for Tomato Plant Fungus

The home gardener must respond quickly to fungus problems in tomato plants or risk losing the year’s tomato crop. Fungal infestations spread rapidly over the plant and are difficult to treat if not caught and stopped immediately. Integrated pest management is an effective combination of preventive cultural practices and use of commercial fungicides. IPM practices encourage gardeners to keep plants healthy using simple techniques and limit the use of commercial fungicides.

Most chemical fungicides work to protect tomatoes from fungus and not cure a plant that is already infected, so cultural practices are important to prevent and stop fungus in the garden. Rotate planting so that tomatoes are planted in the same place only once every three years. Plant tomatoes in a sunny location. Water with a soaker hose rather than a sprinkler for two reasons: fungal spores germinate and grow on wet leaves and water hitting the ground can cause fungal spores to splash up onto the plants. Use plastic sheets or four inches of organic mulch to keep fungal spores in the soil from splashing onto the tomato plants during rain storms.

Monitor tomato plants to watch for fungal attacks. Look for gray circular spots with a black mark in the center on the leaves. This could be Septoria leaf spot. Large dark-brown spots resembling a target on the leaves and sometimes the fruit could be signs of early blight (Alternaria). A greasy-looking dark green or black spot with a fuzzy white growth underneath the leaf could be late blight (Phytopthera). Remove all diseased leaves, stems and fruit. Remove any old yellow or brown leaves that could encourage fungus. The removed plant material should be destroyed and not composted.

Baking soda spray is reputed to be effective to treat late blight, early blight and other fungus problems. Mix 1 tbsp. baking soda and 2 1/2 tbsp. vegetable oil in one gallon of water. After mixing, add one half tsp. of dish soap. Spray the tomato plant once a week, coating the leaves and stems. Spray after the hottest sun of the day is over. Avoid spraying beneficial insects like lady bugs and dragonflies.

Commercial fungicides containing chlorothalonil, such as Ortho Max Garden Disease Control spray, are effective at stopping fungal problems in tomato plants when used correctly. Always follow the label instructions when using a commercial fungicide. Remove diseased plant material and destroy it before spraying. Completely cover the plant with the spray. Repeat the treatment once a week.

Organizations that certify organic farms often allow the use of copper and lime based fungicides that are commercially available. Gardeners seeking to use only organic products should check the product label for more information. Bonide Copper Dust and Bonide Copper Liquid Concentrate are examples of copper-based fungicides. Always follow label directions when using a commercial fungicide and verify the product against the specific organic standards required.