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Kyle’s News & Reviews

Southern Blight Is Killing Tomato Plants In The Area


I was out at a couple of places Monday looking at tomato plants that are dying.  The disease that I am seeing is called Southern blight which is a soil borne fungus that attacks the plant when conditions are right. According to.apsnet.org the initial symptoms of southern blight is a rapid wilting of the entire plant. 

A water-soaked lesion on the stem near the soil line rapidly expands, turns brown, and girdles the stem. A white mold (mycelium) eventually covers the stem lesion and surrounding moist soil. Small, uniformly round structures about 1/16 inch in diameter, called sclerotia, form on the mycelium. Sclerotia are first white, later becoming brown, and resemble mustard seeds. 

The presence of the white mycelium and sclerotia at stem base of affected plants are very useful characteristics for identifying southern blight. The fungus survives in the soil as sclerotia which may build to high numbers when susceptible plants are cropped repeatedly. After sclerotia germinate, the fungus must first colonize organic debris near the soil surface before the fungus can cause infection. The disease is favored by high humidity and soil moisture and warm to hot temperatures (85-95 F).  

I am sure that with the wet soil, humidity and high temps that we have had over the last couple of days there will be many other cases reported of this disease.  The unfortunate part of contracting this disease is the plant is usually too far gone before it is noticed and it is already dead.  If you notice any of your plants with these symptoms remove the plants immediately and dispose of the debris at a location not close to your garden spot.  

Southern blight is most effectively treated by preventing it with the use of a fungicide.  There are several options for treating southern blight, but they are all extremely expensive and not worth it unless you are a commercial grower.  

I had a grower ask if he could just plant a tomato back in the same place and the answer is no, southern blight can live for several years in the soil profile.  The best way to prevent the disease is to rotate the spot for growing fruiting vegetables with a grass-like plant or corn for example.  If you have any questions or concerns about southern blight or any other problem in your garden call the Extension office at 662-675-2730.  

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