Brian Jarvis Master Gardener
Some of you may have had fungal diseases on your tomatoes or may soon have them, so let's talk about some of them and what to look out for.
First up is Septoria leaf spot. This is a fairly common disease of tomatoes that starts from the soil. Septoria will first show up on the lower leaves of your tomato plant. At first it will be small black spots that will develop a yellowish ring around them. These spots will produce more fungal spores that help the disease spread to other parts of the plant.
To minimize the chance of this fungus developing, if you haven't already done so, put a generous layer of mulch under your plants. Mulch minimizes soil splashing onto the plant, thus minimizing the chance of soil transfer to the plant. Also, prune the lower branches of your tomato plants as they grow. This will also help minimize the migration of this fungus from the soil to the lower leaves of the plant.
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If you see signs of septoria on the lower leaves, cut them off and discard them immediately, at which point you may also begin a treatment program with an organic fungicide such as a copper fungicide.
Southern blight is a nuisance. One day the plant looks healthy, but soon it will turn brown and begin to die. Southern blight is another soil-dwelling fungus that attacks the stems at the soil level. Southern blight thrives in hot, humid environments, like Oklahoma summers.
If you suspect southern blight, check the base of your plant for white mold. Essentially, the disease reduces the plant's ability to absorb water and nutrients, and there is no cure, so you should consider pulling the plant out and planting tomatoes in another part of your garden next year. If you have had southern blight before, you can start a treatment program with a copper fungicide early in the season to minimize the chances of contracting the disease.
Early blight can also affect tomato plants. Early blight appears as small spots about 1.5 cm in diameter on the leaves. You may also see concentric rings around the spots. As the disease spreads higher on the plant, the leaves will begin to fall off. Using a copper fungicide can help minimize the spread of the disease, but if the disease progresses, your only option is to uproot the plant.
Finally, here are some steps you can take to minimize tomato diseases.
1. Place a generous layer of mulch around your plants.
2. Rotate crops at least every three years to minimize disease outbreaks.
3. Water your plants while minimizing soil splashing onto the plants.
4. Keep an eye on your plants. Early detection is key.
5. Use a 10% bleach solution to keep gardening tools clean and minimize the spread of disease through tools.
Follow these steps and you’ll be known as the neighborhood tomato lover. Good luck!
To get answers to all your gardening questions, call the Tulsa Master Gardeners Helpline at 918-746-3701, visit the Diagnostic Center at 4116 E. 15th St., or email us at mg@tulsamastergardeners.org.
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