Many calls have been coming through the office about tomatoes being wilted or starting to yellow and die. If your tomatoes have yet to experience these problems yet, consider yourself lucky, but not out of the woods yet. Throughout the end of spring and into summer, tomato plants can develop some sort of disease or fungus that ends up killing the plant. The first step to fighting these diseases is to know who the enemy is. I am going to describe the current tomato wilts to better prepare y’all. Though they are not curable, they can sometimes be prevented!
“My tomato is wilting from the top down.”
Tomato Spotted Wilt Virus (TSWV) is the number one tomato disease now. It is spread by thrips. Usually, the top of the plant looks stunted or wilted but the leaves are not limp as though they had no water. The young leaves may yellow and have red, brown, or black discolorations in them. These discolorations may form a ring or circle. The veins on the underside of leaves may thicken and turn purple. Green fruit can have raised or flat rings, semi-circles, or circles on them which yellow as the fruit ripens. Some varieties of tomato are resistant to TSWV, although they may not be completely immune. Varieties include Amelia, sold by Harris Moran Seeds and Stiletto, available from Clifton Seed Company or Siegers Seed Company. These varieties are probably not yet available in small quantities, but you can look for plants in the nurseries. Once tomatoes get the disease, there is no control. Spraying for the thrips that spread TSWV is not effective. Bag and destroy infected plants as quickly as possible early in the season to prevent spread. Late in the season you may want to just let the infected plants finish ripening the fruit they have.
“My tomato is wilting. It looks like it is out of water.”
At least three things can cause this – Fusarium wilt, Bacterial wilt or Southern blight. A fungus causes Fusarium wilt. It blocks the water conducting tissues in the plant. The leaves yellow and wilt, often starting at the bottom of the plant. This disease can affect just one side or one to several branches of the plant. The plant can die early producing no fruit. If you cut into the plant, the vascular system (just under the surface of the stem) will be brown. Prevent Fusarium wilt by planting resistant varieties. The ‘F’ after the variety name (like Celebrity VFN) identifies these varieties. Fusarium wilt can survive in the soil. Do not plant tomatoes in infected areas more than once every four years. Rotate tomatoes each year. Do not plant them in the same area that you planted potatoes, eggplant or pepper last season.
Bacterial wilt causes a rapid wilting and death of the plant. The plant dies so quickly it may not have time to turn yellow. To identify Bacterial wilt, cut through the stem. Bacteria wilt browns the pith or middle of the stem. On bad infections, the pith may be hollow. Cut a short section of the stem and suspend it in a clear glass of water. You can often see a milky, bacterial ooze streaming out of the bottom of the cut stem. There are no controls or resistant varieties for bacterial wilt. It also attacks peppers, potatoes, and eggplant. Carefully dig out infected plants and soil and discard. Do not plant any of these vegetables in this area for at least four years.
Southern blight is a white mold that rots the stem at or near the soil line. The plant is stunted, wilts or dies. Look for the cottony fungus growth and the light brown BB sized fruiting structures of the fungus. The fungus may be at or slightly above or below the soil line. You may not see the white fungus growth if the weather is dry, even though the plant may still be infected. Bury all plant residues before planting, plant vegetables farther apart, and treat with Terraclor at planting if you have a problem with Southern blight. Some people wrap the stem near the soil line with foil to slow this disease.
Tomato wilt can be devastating, but you can learn to live with it. Hopefully this knowledge of the wilts will help you identify what is happening to your tomatoes and put into place practices and preventive measures.
Joke of the Week: What is a Tomato’s favorite book? “Uncle TOM-ato’s Cabin”