Tomato Septoria Leaf Spot

tomato septoria leaf spot

Septoria leaf spot is one of the most devastating diseases that can affect tomato plants. It can kill the leaves and stems and reduce the quality of your tomato crop, so treatment and prevention is extremely important.

Causes and Symptoms

Septoria leaf spot is caused by septoria lycopersici, a fungus that lives in the soil near tomato plants or on weeds that can grow in gardens. The fungus creates spores that are carried by wind and rain to uninfected plants. The fungus causes deterioration of the plant foliage.

Once a plant has been infected with it, the leaves will begin to show random wet-looking spots all over, which will grow to a larger size and change to a light brown or tan color. The leaves may even have small spore-producing masses on the spots. As the infection worsens, the leaves will die and fall to the ground.

Treatments and Control

There are many methods available to treat and control septoria leaf spot on tomato plants. It is recommended that you engage in what is known as clean cultivation, in which you inspect your plants and remove the sick and dead ones from your garden. It is preferable, when these plants are removed, that you use them to make compost so that nutrients are put back into the soil.

Tomato fungicides are another option for treatment. These should be mixed with water and sprayed all over the plants in the morning and before and after it rains. You can also buy ready-made fungicide sprays for tomatoes and use them in the same way. These products are best used before disease sets in, but are also useful after the first signs of disease. Many of the best fungicide products contain copper, which is extremely toxic to the fungus and rapidly kills it.

Once treatment has been applied, it is imperative to control the spread of the disease and prevent any recurrences. Here are steps you can take when caring for your tomato plants.

  1. Use a control method to keep weeds at bay. Since septoria lycopersici is found on horse nettle and jimsonweed, keep your garden free of these.

  2. For preventative purposes, try to plant your tomatoes early in the season, since the fungus is less likely to thrive in colder temperatures, or you can try rotating your plants so that you only plant tomatoes in one spot in your garden once every few years.

  3. Mulching can be used as an effective preventative as well, since it is a way to keep potentially infected soil from coming into contact with your plants.

  4. You should not handle your tomato plants when they are wet, and be careful not to water them too much, as too much moisture invites fungus. Watering your tomato plants every few days, as opposed to every day, will provide them adequate moisture and discourage fungus infestation.

Comments from Other Gardeners
  • john says:

    do not use thrown away plants in your compost pile

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