Tomatoes are a popular summer fruit, but they are susceptible to fungal, bacterial and viral diseases.
Fortunately, growers can take preventive steps to minimize the spread of these diseases, said Amy Timmerman, University of Nebraska-Lincoln Extension educator in plant pathology. Here are nine steps she recommends.
1) Plant disease-resistant tomato varieties. These varieties will be labeled as such at the store. Heirloom tomatoes, which recently have gained popularity because of their taste, aren't disease resistant, Timmerman said.
2) Keep proper sanitation by removing dead plants and tilling the soil each fall and spring. Tilling the soil helps reduce the number of surviving fungi, bacteria and viruses. "The microbes in the soil will eat the plant debris and fungi and bacteria," Timmerman said.
3) Rotate the crops to different areas of the garden. People should plant tomatoes in a different spot of the garden each year. In addition, avoid planting eggplants and peppers in the same area that tomatoes were planted the year before, because these plants are vulnerable to the same diseases.
4) Apply grass clippings or organic mulches to keep fungal spores or bacteria, which often reside in the soil, from infecting the plant. When the tomato plants are watered from above with hoses or rain, the water may splash bacteria and spores from the soil to the leaves, thus infecting the plant.
5) Use soaker hoses to water tomato plants instead of watering from above. This practice helps prevent water from splashing bacteria or fungal spores from the soil to the plant leaves.
6) Don't overcrowd tomato plants. Take into account how wide the plants will grow -- usually up to 2 feet on each side -- and space them out accordingly. The spacing allows for air movement so the plants can dry out. "Because spores need water to germinate and to move," Timmerman said, "so the sooner you can dry them off, the better off you are."
7) Avoid working among the tomato plants when they're wet, either with dew or from watering. Fungal spores and bacteria move around easier when it's wet, Timmerman said.
8) When caging tomatoes, clean the cages with bleach or isopropyl alcohol to kill bacteria on the cages and reduce the risk of infecting the plant.
9) If disease spots start appearing on tomato leaves -- and they always start with the lower ones first -- pinch off the infected leaves to minimize the spreading of the disease. Timmerman said tomato plants can still bear good fruit even if they lose leaves from as much as 8 inches from bottom of the plant stem.
Identifying the disease can be helpful to finding the right treatment. If the plant is infected with a fungal disease such as early blight and septoria leaf spot, fungicide will help control the disease. Timmerman said she recommends a copper-based or Bordeaux fungicide because those are organic.
However, if the plant is infected with bacterial or viral diseases, the plant can't be saved, so the best thing to stop the spread of disease is to remove the plant from the garden.
For more information on how to identify and manage fungal, bacterial and viral diseases for tomatoes, consult UNL Extension Circular 1864: Leaf and Fruit Diseases of Tomatoes at http://www.ianrpubs.unl.edu/sendIt/ec1864.pdf or from a local UNL Extension office.