Maybe monsoon season is over and maybe not, but one thing we know for sure… with all this water and heat, we will be in the midst of a perfect storm for fungal diseases on our plants, this is especially true with tomatoes. .

Fungal diseases are one of the primary problems with growing tomatoes. Of course there are insects, four-legged furry tree rats, and birds that like to dine on our tomatoes, but a fungal disease will take down the entire plant rather than attacking just a few of the fruits. So, let’s talk about fungal disease in tomatoes and what you can do about it.

The first thing we need to talk about is the disease triangle. As we know a triangle is a shape with three sides. For our purposes, the triangle serves as a way to think about plant disease because for your plant to have a disease, you the presence of three elements: the plant, the environment, and the disease. If you remove one of these, you minimize your opportunity for disease.

If you are growing tomatoes – you have the plant. If your tomatoes are planted in soil (like they all are) you likely have the presence of a soil-borne fungal disease. In this scenario, you primary defense strategy for preventing disease in your tomato is to manage the environment in which they live.

Since most of the fungal diseases that affect tomatoes are present in the soil, your first defensive strategy should be to add a layer of mulch around your tomato plants. Mulch helps to create a barrier between the soil and the leaves on your plant by minimizing splashing of soil up onto the plant.

Secondly, you can trim up the leaves on your tomato plant so that there are no leaves one foot above the ground. This helps minimize the opportunity for disease to land on the leaves if it does splash.

Next, you can plant your plants according to directions. Tomatoes typically like to be planted about 3 feet apart. You can plant them closer, but this crowding will decrease ventilation which will contribute to creating an environment favorable to disease development. So, giving your plants proper spacing will help minimize the opportunity for disease.

Septoria Leaf Spot is one of the more common diseases of tomatoes. You will likely notice it first on the lower leaves of the plant, because it splashes up there from the soil. From there, splashing water and rain can help it move up the plant. We can also spread this disease by using pruners on an infected plant and then using them on a plant that isn’t infected. So, keep those pruners cleaned by cleaning them with a 10% bleach solution.

If you find Septoria on your plants, start by trimming off the infected branches. This will help prevent the migration to the rest of the plant. It would also be a good idea to start using an anti-fungal like organic copper fungicide. Spray according to directions.

Southern Blight is one we’ve experienced at our Seed to Supper farm. The problem with this one is that you won’t see it (at least we didn’t) until it’s too late. Southern blight essentially establishes itself right at soil level on the plant. As it grows, it destroys that part of the plant which allows the plant to draw up nutrients and water, so the plant dies pretty quick. You’ll know it’s Southern blight by the white substance growing on the plant at root level. Your solution for this is to pull the plant and begin a fungicide treatment program on nearby plants to try to minimize the spread of the disease.

There are a variety of other fungal diseases that affect tomatoes but here’s a list of practices that can help to minimize these diseases in your garden.

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. And watering in the morning can also help since your plants won’t be wet all night long.

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.

If you follow these steps, you will be well on your way to a successful year growing tomatoes. 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: Tom Ingram