Tomato Challenges

Sunday, June 24, 2018 2:36 PM

This time of year, we get a lot of questions about one of our favorite garden crops: tomatoes. We love our tomatoes, but there are a variety of challenges associated with growing them.

One of those challenges is Septoria leaf spot. Septoria leaf spot is a very common fungal disease here in Oklahoma. Starting at the bottom of your plant, you will notice leaves with yellow areas that become circular with grayish centers and dark borders. The spores from septoria can be quite aggressive, spreading upward throughout the plant.

When you see this, it’s time to begin a fungicidal spray program of copper fungicide on a 7 to 14 day schedule. This will not cure the infected leaves but will diminish its ability to spread. Infected leaves should be removed.

Also, to minimize exposure and spreading of fungal diseases, tomatoes should not be watered via an overhead sprinkler system, as the splashing water tends to provide a means through which the disease can migrate. Drip irrigation is preferable in most instances.

If you are having problems with fungal diseases, be sure you are rotating your crops. Planting the same crop in the same spot year after year tends to encourage these fungal diseases to develop. However, when rotating crops with tomatoes, do not put peppers, eggplants, or potatoes in the same rotation as they all tend to be susceptible to many of the same diseases.

Another common challenge to growing tomatoes successfully is blossom end rot. Symptoms manifest in an expanding, tan, water-soaked area of the blossom end of the fruit. Blossom-end rot is a complex disorder, which is thought to be caused by a calcium deficiency. However, the solution is not often as simple as adding calcium to the soil.

High temperatures and wind, fluctuating water availability, and a little drought stress thrown in (sounds like Oklahoma) create an environment in which you may see blossom-end rot. Somewhat ironically, excessive soil moisture for a long period of time can also contribute to this problem, as it tends to damage the root system and diminish the plants ability to uptake calcium. Excessive fertilization with nitrogen can also be a contributing factor.

Just remember, calcium deficiency is rarely a direct cause of blossom-end rot. It is kind of like having a fever is not the problem but instead an indicator of a problem. Adding calcium can be of little value if the blossom-end rot is the result of the environmental conditions mentioned above.

These are only two of the many challenges we face growing tomatoes. You can find several relevant fact sheets on the topic by visiting the Lawn & Garden page of our website and then clicking on “vegetables.”

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at