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.

  • Powdery 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 spots.
  • 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.
  • Anthracnose, 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.
  • Fusarium 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.

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.

Bordeaux Mixture

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.