Tomato Update

I've been fielding lots of tomato questions in the clinic lately. The top four questions and their answers
follow:

My tomato plants were doing great but then the entire plant suddenly wilted. What’s happened?

Southern bacterial wilt and to a lesser extent southern stem rot are the most common culprits. If you cut the bark off of the stem and see brown discoloration in the vascular tissue, southern bacterial wilt is the culprit. If white fungal growth is visible at the base of the plant, it is likely to be southern stem rot. There is no cure for either of these diseases because both are caused by organisms that live in the soil for years. Pull up and destroy any affected plants. Rotate your tomatoes to another spot in the garden or relocate your garden altogether. If this is not possible, consider growing tomatoes in containers starting with clean, bagged soil or potting mix.


My tomatoes seem to have stopped growing and are starting to look stunted. The young leaves are purplish-brown and appear to be dying. What’s going on?

This could be a viral disease called tomato spotted wilt virus (TSWV). The disease is transmitted to the tomato plants by tiny insects called thrips. The symptoms usually appear first at the top of the plant but eventually spread. There is no cure for this disease either. Remove infected plants from the garden. Eliminate weeds in and around the garden that may harbor thrips. We only have one flush of thrips annually here so you can go ahead and replant tomatoes in your fall garden without fear of the disease returning. There are several TSWV resistant varieties of tomatoes available including Amelia, Crista and Talledega.

Why are my tomatoes flowering but not setting fruit?

Tomato pollination and fruit set occurs best when night temperatures are between 60 and 70 F. When night temperatures consistently stay in the mid-seventies or higher, fruit set will diminish dramatically.

What causes rot on the blossom end of my tomatoes?

“Blossom end rot” is a disease that occurs when tomato plants cannot move enough calcium out of the soil. If blossom end rot is a problem in your garden, make sure you sample your soil and lime according to the sample recommendation. Blossom end rot can occur even with adequate soil calcium levels if the plant is not able to take up the calcium efficiently. This can occur during a drought if plants aren’t watered regularly.

I have also seen several tomato plants (and other crops) that have been damaged by herbicides. Tomatoes are very sensitive to certain chemicals including glyphosate. Take special care when using herbicides around the garden and remember that herbicides can drift if the wind is blowing or volatilize if temperatures are high. Herbicide injury frequently results in abnormal “strappy” growth, marginal burn on the leaves or discoloration of the veins of the leaf.

I am seeing a fair number of aphids on tomatoes. This is probably because of the stress the plants are under due to the drought. Aphids can be easily controlled with insecticidal soap, just make sure that you treat the underside of the leaf and the new growth where most of the aphids are found.