Sunday, June 24, 2018 By: Ask A Master Gardener

Tomato Growing Challenges in Oklahoma

Tomato Growing Challenges
Brian Jervis: Ask a Master Gardener

Sunday, June 24, 2018

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 common fungal disease 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 plant’s 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 similar to how a fever is an indicator of a problem and not the actual problem. Adding calcium can be of little value if the blossom-end rot is the result of 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.”
Garden tips
  • Vigorous, unwanted limbs should be removed or shortened on new trees. Watch for forks in the main trunk, and remove the least desirable trunk as soon as it is noticed.
  • Most varieties of mums are more productive if “pinched back” now. Either pinch off with fingers or cut to remove an inch or so of limb tips above a leaf. This results in the growth of new limbs and a fuller plant. Do not pinch after mid-July or it will interfere with fall blooming.
  • Watch for tiny, sap-sucking insects called aphids on roses, perennial flowers, shrubs and vegetables (especially tomatoes). They produce a sticky substance called “honeydew." Many can be dislodged with a hard spray from your garden hose or two applications of insecticidal soap will usually greatly reduce any aphid damage to your plants.
  • Crapemyrtles are one of the few shrubs that should be planted in the middle of summer. Growth of new roots of these plants occurs best with summer soil temperatures.


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