To diagnose tomato fungal diseases, look for rotten-looking spots in humid weather, especially if it has been raining or you've been watering your tomatoes (Lycopericon esculentum) with sprinklers. No fungal disease is limited strictly to tomatoes. The same fungal diseases that strike tomatoes strike other plants. Turn to simple homemade fungicides to help get rid of the problem.
Fungal Diseases Found on Tomatoes
When the weather is hot, watch for the telltale spots of these fungal diseases that often strike tomatoes.
mildew (Leveillula taurica) causes
irregular, bright-yellow blotches on leaves. The blotches develop dead spots
surrounded by a yellow halos. White spores form on the tops or bottoms of the
leaves. Powdery mildew eventually kills the leaves, weakening the plant and
causing sunburned tomatoes.
- Early blight, caused by the fungus
Alternaria solani, appears as spots with concentric rings and surrounded by
yellow on leaves, stems and tomatoes. Early blight can kill much of the leaves and cause tomatoes to drop.
- Late blight, caused by
the fungus Phytophthora infestans, typically starts in cool weather, forming
dark, water-soaked spots with white mold on the edges. Late blight can turn leaves
and stems completely brown within two weeks. Infected tomatoes develop shiny dark
- Septoria (Septoria lycopersici) typically appears when it has rained or you're using
sprinklers and the temperatures are between 68 and 77 degrees
Fahrenheit. After the plants begin to set tomatoes, small beige spots with dark
borders appear on leaves near the ground. The leaves turn yellow and fall off.
The weakened plant produces smaller, poorer quality tomatoes.
- Leaf mold,
caused by the fungus Passalora fulfa, forms yellowish or pale green spots on the
tops of leaves. As the top leaves grow, turning more yellow, a gray, velvety
mass of spores grow on the bottoms of the leaves. It can also attack blossoms,
stems and tomatoes. It starts in warm weather with high humidity.
caused by the fungus Colletotrichum coccoides, causes small rounded dents on
tomatoes that grow larger and spread deeper. This fungus also appears in warm,
humid weather with sprinkler watering or rainfall.
wilt (Fusarium oxysporum) spreads upward from the soil,
causing drooping plants and wilting, yellow leaves, sometimes on just one side
of the stem.
Fungicides for Powdery Mildew
Try apple cider vinegar or milk to treat powdery mildew and other fungal diseases.
Mix 2 to 3 tablespoons of 5 percent acidic apple cider vinegar in 1 gallon of water. Pour into a garden sprayer and spray on the leaves during the cool hours of morning.
Don't add more vinegar thinking it will work better -- apple cider vinegar can kill your tomatoes if the mixture is too strong.
Spray a mixture of 1 ounce of milk to 9 ounces of water every three to four days when you first spot signs of powdery mildew on your plants.
More Homemade Fungicides
To prevent or treat fungal diseases, spray plants the tops and bottoms of the leaves twice a week during wet weather and once each week during dry conditions with a 3 percent solution of hydrogen peroxide, which you can buy at most drug stores. Check the label on the hydrogen peroxide, but there's usually no need to dilute the standard drugstore type. Do not spray young seedlings with this mixture as it can potentially kill them. Use this mixture only on established plants.
Finely chop 1 garlic bulb, 2 tablespoons of canola oil, 4 hot peppers and 1 lemon in a blender. Steep this mixture overnight then strain it through cheesecloth or other fine strainer. Add 4 tablespoons of this mixture in 1 gallon of water, pour it into a sprayer and use it when you spot symptoms of fungal disease, spraying tops and bottom of the foliage.
To make a fungicide from cornmeal, soak 1 cup of whole, ground cornmeal in 5 gallons of water then strain the solids. Spray the milky juice on tomato leaves.
Finely chop 1 cup of horseradish roots in a food processor and soak it in 16 ounces of water for 24 hours. Strain the liquid, mix it with 2 quarts of water, put it in a sprayer and spray it on the leaves.
Always test any homemade mixture on a small section of the foliage before spraying the entire plant. Wait at least 24 hours and check for damage before applying to the entire plant.
Do not spray these homemade mixtures when temperatures are above 85 degrees Fahrenheit, conditions are sunny and wait for the cooler portions of the day to apply to lessen the chance of burning.
While the term "homemade" suggests household ingredients, perhaps the best organically approved fungicide you can make at home to treat a wide variety of fungal disease on tomatoes uses ingredients that you can buy at most garden supply centers. The Bordeaux mixture is especially useful for treating early and late blight in addition to powdery mildew and other fungal infections.
To make a Bordeaux mixture appropriate for home garden use, mix 3 tablespoons of hydrated lime with 1 pint of water. Separately, mix 6 1/2 tablespoons of copper sulfate in another pint of water. Filter each of these through cheesecloth or other loosely woven cloth to remove particles that might clog a sprayer nozzle. Pour the copper sulfate solution into the garden sprayer tank then the hydrated lime solution then another 3 pints of water.
Shake the tank frequently while you spray the tomatoes.
- Dirt Doctor: Organic Recipes Homemade
- Golden Harvest Organics: Plant Disease
- Fine Gardening: 35 Pest and Disease Remedies
- University of Nebraska Extension: Leaf and Fruit Diseases of Tomato
- Sustainable Gardening Australia: Early Blight of Tomatoes
- Growing a Greener World: Controlling or Eliminating Powdery Mildew
- University of California IPM: Powdery Mildew on Field-Grown Tomatoes
A one-time farm boy, Richard Hoyt, holder of a PhD in American studies, is a former newspaper reporter, magazine writer and college professor. While writing 27 novels of suspense, he has lived on sugar cane, pepper and papaya plantations and helped keep bees in Belize.