I have been growing tomatoes for more than ten years. One of the most common problems for every tomato gardener is septoria leaf spot disease. So we will talk about a disease that a lot of tomato gardeners complain about. Septoria leaf spot is a disease that is actually caused by the fungus Septoria lycopersici, so this is a fungus attack disease. How do you know that your tomato plant is infected with septoria leaf spot? You will notice that in the lower canopy there is some complete browning of the leaves. In those brown leaves, you will see some individual small, roughly circular leaf spots, and you will notice lots of them. These leaf spots are the cause of the leaves turning brown. The main problem is that the disease can kill many leaves, and you will lose a lot of carbohydrate sources for fruit, and as a result, you will have less yield. It is definitely a disease you want to control, but there is no cure or variety resistance for these plants. You can buy other disease-resistant plants, but not for septoria leaf spot. Researchers are still trying to create a tomato variety that is resistant to septoria leaf spot.