What is Septoria Leaf Spot on Tomatoes?

Septoria Leaf Spot on Tomatoes is a disease of the leaves of the tomato and doesn't occur on the fruit, however it does affect the fruit.

The disease comes from a fungus on the leaves and creates small circular spots less than 1/8 of an inch in diameter on the undersides of the plants older leaves. As the spots grow, they enlarge to about a quarter of an inch in diameter. They have a gray or tannish center and darker brown margins.

While they look like early blight, another disease of tomato plants, you can differentiate it from early blight as the spots grow and coalesce. They develop pimples in the center that are dark brown, unlike blight. These are the pycnidia-fruiting bodies. You also might see the spots on the plant blossoms, the calyxes and stems of the plant. It seldom grows on the tomatoes. Instead, it kills the fruit by after a plant has severe infection, by causing leaves to wither up and drop. This leaves the fruit unprotected from sunscalding.

The symptoms of infection can appear at any time, but normally you notice it occurring when the plant is fruiting. It normally starts on the lower leaves, which as stated before are the older leaves. It needs moist, damp days with temperatures between 59 degrees and 80 degrees to grow. The optimal temperature for this type of disease is 77 degrees Fahrenheit.

What Causes Septoria Leaf Spot on tomatoes?

As mentioned earlier it is a fungus that preys on not just the tomato plant but also the potato and eggplant. As with most fungi, it needs damp conditions to grow and a specific temperature to optimize that growth.

The spores travel by splashing rain, windblown water, insects, on the clothing and hands of gardeners and on their equipment. While it isn't a soil borne fungus, it's best to rotate crops if you have it one season since the debris from infected plants from the previous year might be in the soil.

Cures for Septoria Leaf Spot on tomatoes

Organic Methods

The best method to control the fungus is preventative. Don't give it room to start developing. Since it requires moisture to grow, do what you can to prevent lingering moisture on the leaves of the plant. Water in the morning. Don't water from overhead. This not only makes the leaves damp, the water splashing might transfer the fungi spores to other plants. Immediately remove infected garden debris and dispose of it properly. When you plant, make certain you have enough space around your plants so they have adequate circulation. This allows the leaves to dry.

Since the fungus affects weeds such as horse nettle, ground cherry, and black nightshade, keep your garden free of weeds and eliminate all weeds before you plant. In addition, there is some speculation that the seeds of the tomato might carry the disease. Get your seeds from a reputable greenhouse or other source to make sure they're disease free. You'll also find some types of tomatoes are resistant to this fungus. If you have had a severe outbreak in the past, consider using these for a year. It normally takes one year with no outbreak to clear the area of the fungus.

Fungicides

If you have a severe problem, which is causes loss of your tomato plants and therefore crop, you might consider using a fungicide to control it. Use fungicides that are safe for use on tomatoes. A few examples are maneb, cholorthalonil, mancozeb and benomyl. The fungicide Captan has not proven effective against Septoria leaf spot on tomatoes.

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