Tomato Plant Fungal Diseases

Learn what to do about fungal diseases before they destroy your tomato crop.

Excerpt from the Popular Farming Series magabook Organic Farm & Garden with permission from its publisher, BowTie magazines, a division of BowTie Inc. Purchase Organic Farm & Garden here.


Tomatoes are prone to several fungal diseases that can slowly destroy an entire crop. Often the diseases start late in the season and the tomato plants don’t succumb until the harvest is finished. But sometimes especially during damp, muggy summers – fungal diseases can strike earlier.

Early blight, late blight and Septoria leaf spot all have their own characteristics, but each disease usually starts with wilted, yellow-colored leaves sometimes with black, brown or gray spots at the bottom of the tomato plant. If unchecked, the fungus creeps slowly upward until the entire tomato vine wilts.

Prevent fungal disease with good gardening practices. Rotate crops to keep tomato plants away from the previous seasons’ fungal spores. Allow space for air circulation between plants and water your tomatoes’ roots, not their leaves.

At the first sign of a fungal disease, pluck off yellowing leaves from the bottom of the tomato plant, taking care not to touch healthy foliage. When finished, don’t compost the diseased foliage, as fungal spores are likely to survive and come back to haunt you in seasons to come. Burn them or toss them out with the garbage.

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As a last resort, gardeners can look to fungicides, but even organically approved substances containing sulfur and copper are frowned upon because they can damage plants and soil organisms.

Work doesn’t stop at the end of the season; remove and discard crop residue to avoid any chance of recurring diseases, then plant a cover crop, such as winter rye or nitrogen-fixing hairy vetch. Tomatoes, peppers, potatoes and eggplants are all members of the Solanacaea, or nightshade, family and share many common pests and diseases. Avoid planting any of these crops where they were grown the previous two seasons.


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