Fungus is an organism that reproduces and spreads by spores, and feeds off the living tissue of the tomato plant. This causes the plant to lose vitality, to discolor or become disfigured and eventually to die. Common fungal diseases of tomatoes include septoria leaf spot, early blight, anthracnose, fusarium wilt, verticillium wilt and late blight. A preventative program for fungal problems on tomatoes can be more successful than disease treatment.
Organic Soil and Tomato Varieties
Use of compost is a preventative measure for tomato fungus problems. Healthy soil creates healthy tomato plants that are more able to resist fungal disease. Compost adds billions of microorganisms to the soil. Microorganisms release nutrients into the soil that in turn feed the plant. Healthy plant growth is the best prevention for fungal problems. Choose tomato varieties that are known as disease resistant. The National Sustainable Agricultural Information Service recommends using tomato varieties such as 'Mountain Pride,' 'Supreme,' 'Gold,' 'Fresh' and 'Belle.'
Tomato fungal problems are reduced by companion planting. Plants interact and create mutually beneficial supportive environments. The science of companion planting has identified many plant combinations that increase disease resistance. The onion family, nasturtiums, marigolds, asparagus, carrot, parsley and cucumber are good companion plants for tomatoes.
Air and Watering
Fungus spores spread on air and water. Tomato plants need good air circulation. Give plants 2 to 3 feet of space between rows and plants. Pull weeds immediately and clean up all plant debris on the ground around tomatoes. Keep a 3-inch layer of mulch around the base of the plants to prevent excessive soil dampness. Mulching reduces direct contact of fungal spores with soil. Drip irrigation is a preventative measure for fungal disease. Fungal spores are spread by water onto tomato leaves. Reduce water splash by using a drip method, soaker hose or careful hand watering around the base of the plant. Do not water tomatoes in the evening.
Natural Fungal Sprays
Copper and sulfur-based fungal sprays are the only ones allowed in organic certification programs. For home gardens, tomato fungal problems can be controlled with sprays of hydrogen peroxide, watered compost tea and baking soda. Nettle tea and comfrey tea are also effective foliar sprays. Corn and garlic combination spray is effective as a fungus preventative.