We’re at the point where some of you either have had or might have fungal disease in your tomatoes on the horizon. So, let’s talk about some of those diseases and what you should be looking for.

First up is septoria leaf spot. This one is a fairly common disease of tomatoes and originates in the soil. You’ll likely notice septoria first on the lower leaves of your tomato plant. They start as small, dark spots but develop a yellowish halo around them. These spots are where more fungal spores are generated helping the disease to spread to other parts of the plant.

To minimize your chances of this one (if you haven’t already) place a good layer of mulch under your plants. The mulch will help minimize splashing of soil up onto the plant which will in turn minimize its ability to transfer to the plant. Also, as your tomato plants grow, prune off those lower branches. Again, this will help to minimize migration of this fungus from the soil to the lower leaves of your plant.

As soon as you see signs of septoria on those lower leaves, prune them off and throw them away. At that point it’s also good to start a treatment program with an organic fungicide such as copper fungicide.

Southern blight is a mean one since one day your plant will look healthy and then rather quickly it turns brown and begins to wilt. Southern blight is another fungus that lives in the soil, and it attacks the stem right there at the soil level. Southern blight thrives in hot, humid conditions which sounds like summer in Oklahoma.

If you suspect southern blight, look at the base of your plant for a white-looking mold. Essentially, this disease reduces the ability of the plant to uptake water and nutrients and there is no cure, so you’ll need to pull the plant and think about planting tomatoes in a different place in your garden next year. If you’ve had southern blight before, you can begin a copper fungicide treatment program early in the season as a way to help minimize your chances for this disease.

Early blight is another one that can affect tomato plants. With early blight, you’ll notice spots on the leaves that are about 1/2 inch in diameter. You also might notice what looks like concentric rings around these spots. As the disease moves up the plant, it begins to defoliate. Copper fungicide can help to minimize it’s spread but if it gets ahead of you, you’ll just need to pull the plant.

Ultimately, here are some steps you can take to help minimize disease in your tomato plants.

1) Apply a good layer of mulch around your plants.

2) Rotate your crops every 3 years at a minimum to minimize disease build up.

3) Water your plants in a manner that will minimize splashing of soil up onto your plant.

4) Keep your eyes on your plants. Early detection is key.

5) Keep your garden tools clean by using a 10% bleach solution to minimize spreading the disease via your tools.

Following these steps should help you to be known as the tomato person that lives in the neighborhood. Good luck!

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 mg@tulsamastergardeners.org. Photo: Edward Sikora, Auburn University, Bugwood.org