Tomato Diseases
By: Dale Mermoud, Master Gardener

You've planted your tomatoes and everything looks great! The problem is keeping them in this great disease-free condition during the growing season. Your next purchase and probably your largest expense is the purchase of an insecticide and a fungicide for your tomatoes.

There are many diseases that can affect your tomatoes. This article will cover some of the more common diseases as well as cultural practices and/or fungicides to use for control. Tomato diseases are somewhat hard to separate because they cause similar symptoms in the plant.

An example of soil-borne diseases are fusarium wilt and verticillium wilt. These diseases cause the plant to wilt because the water-conducting tissues of the stem are plugged. Control of these diseases requires soil fumigation and is impractical for the homeowner. You can minimize these diseases by removing and destroying last year's tomato plants, by purchasing resistant varieties, and by planting in a different garden location from where last year's tomatoes were grown.

Other diseases controlled by a regular fungicide spray program are early blight, late blight, septoria leaf spot and anthracnose. Plant viruses such as tobacco mosaic can weaken the plant and cause reduced fruit quality.

Early blight is a fungus disease prevalent from May to June. Late blight occurs later in the season from August to September. Brown spots first appear on the leaves, these spots cause the leaf to yellow, turn brown and shrivel defoliating the plant as the fungus spreads upward. You can reduce this disease by mulching around the plant when planted to minimize splashing the fungus from the soil or host weeds during rain. Use trickle and/or drip irrigation to eliminate the splashing action of sprinklers. Also start a fungicide spray program at planting time.

Septoria leaf spot occurs during the summer and are small circular spots 1/8 inch in diameter. They will defoliate the plant, therefore fungicide protection is necessary. Continue the fungicide application schedule you started at planting time.

Anthracnose is a fungus disease affecting the fruit and may lead to fruit rot, especially on unsupported plants. Minimize this disease by staking and/or tying your plants.

Tobacco mosaic virus comes in various strains and can infect tomatoes, peppers, eggplant, petunias and weeds such as poke and horsenettle. This disease causes splotchy yellow to white patches on the ripening fruit. This disease can be minimized by controlling insects--particularly aphids--eliminating weed hosts of the disease, no smoking and/or tobacco use when handling tomato plants and good sanitation, i.e. clean hands and tools when tying and/or pruning tomatoes, then cleaning hands and tools before working with other susceptible plants.

Fungicides to be used for tomatoes are mancozeb, benomyl and chlorothalonil. Start a spray program at planting and continue it until harvest. Follow label directions for amount to use and intervals from the last spray. There is no reason why you cannot have green, healthy, alive plants the whole growing season! For more information contact your University of Missouri Extension Center and ask for MU Guide 6370 and 6461.