Tomato alternaria canker is a bacterial fungus that can cause significant damage the stems, leaves and fruit of the tomato plant. Once a plant is infected, it is difficult to eliminate, but there are ways to minimize the damage.
Causes and Symptoms
Alternaria needs moisture to survive, and thrives in areas with humid climates, or where there has been significant rainfall. It lives in the seeds and seedlings, and is also spread by spores, as they become airborne and land on plants. Alternaria canker flourishes in dead plants that have been left in the garden during the winter. When dead debris is added to a compost pile, it can spread to other vegetables throughout the garden. It is made worse by the fact that the fungus grows so slowly that its presence will often only become apparent when seedlings become larger, and are transplanted into the garden.
As the tomato alternaria canker spreads throughout each plant, the lower leaves will begin to turn yellow, and develop dark colored spots. These become progressively larger, until they cover the leaves entirely, causing them to die and drop to the ground. This fungus also causes rings to form around the stem of the plant and suffocates it, until the stem withers and collapses. The tomato fruit is affected as well, with brown cankers dotting them and making them inedible. Once the disease has spread to this point, little can be done to save the tomato plant.
Treatments and Control
A good irrigation system will decrease the chance of alternaria infecting tomato plants. Overhead irrigation systems should never be used on tomatoes though, as they cause the plants to remain wet, allowing the fungus to grow. Drip irrigation in the best system to use, as it keeps the roots wet, yet allows the rest of the plants to remain dry. Usually one irrigation tube is all that is needed for each row of tomato plants.
For plants that have already become infected, it may be necessary to use a fungicide spray to save them. While the disease cannot be completely eradicated, it can be controlled through spraying. There are several commercial fungicides available. Preparations containing mancozeb are particularly effective, as are copper sprays for tomatoes. Chlorothalonil, mandipropamid and fluopicolide are effective fungicide ingredients, when treating the disease in later stages. A natural fungicide can be made using baking soda, vegetable oil and castile soap mixed in water. This mixture has been shown to be effective in treating several fungal diseases. Any fungicide used will need to applied on an ongoing basis, though. One spraying will not be sufficient to treat tomato alternaria cankers.