What Causes Brown Spots on Tomato Leaves?

Q. What is causing brown spots and leaf scorch on my tomato plants? I grow about 17 different tomato plants and several different varieties in containers. I always use good potting soil and compost each year in the containers. They are drip irrigated.

A. This is the time of year that brown spots begin to develop on tomato leaves. As the season progresses, disease problems on tomatoes are often in inevitable. Prevention of disease should be high on your list of things to do with tomato plants.

            It’s too late this season but some varieties are more susceptible to diseases than others. If you don’t know which variety you have, do a little homework and pick varieties more resistant to disease that give you the types of fruit you like.

            Tomato cages are nice. They support the fruit off of the ground. Fruit lying on the ground is more likely to rot than fruit supported off of the ground.

The beginnings of tomato disease probably early blight

            Tomato cages can also be a menace. They force crowding of the interior of the plant. Leaves and vines growing in the center don’t receive enough sunlight to stay healthy. They also don’t provide good air circulation. This encourages disease. Remove the oldest leaves near the center of the plant to improve air circulation and reduce disease problems.

            Drip irrigation is good. Watering at the base of the plant helps. Many vegetable plants, unlike us, don’t like showers. Avoid overhead watering of these plants. Overhead watering keeps the center of the plant wet which encourages disease. Splashing water can spread disease from leaf to leaf.

            Regular feeding of plants is important. When fruit has set then continue monthly feeding of tomato plants. They are taking nutrients from the soil as they grow. You should be replacing these nutrients as they are removed.

            At the first sign of possible disease it is important to take action. Applications of fungicides may be your last alternative. Choose a fungicide for controlling the more common tomato diseases such as early blight. Most fungicides are preventive and don’t cure a disease once they have begun and running rampant.