Septoria Leaf Spot

• Septoria leaf spot can overwinter in tomato plant debris and germinate when conditions are favorable. The disease quickly spreads when temperatures are between 60 to 80 degrees Fahrenheit, according to Virginia Cooperative Extension. As the disease progresses, it moves up the stems of tomato plants and causes leaf problems. Early signs of the disease may be mistaken for tomato spot disease, but differ because you can see the black fungal spores in the center of the gray spots.
  
  

Damage

• Gardeners may notice water soaked spots appearing after the fruit has set for the growing season. Yellowing appears around the spots.These spots begin to enlarge to 1/4 of an inch in diameter. The center of the spots can be gray, brown or black. As the disease worsens on the leaves, the tomato plant starts to defoliate. Defoliation disrupts the tomato plant's ability to photosynthesize and make nutrients. Because photosynthesis is being compromised, the tomato may produce less fruit or the fruit may get sunburned.
  
  

Management

• You can manage the disease by removing all diseased tomato plant debris before winter. Rake up leaves, stems, fruit and foliage. Septoria leaf spot can grow on surrounding weeds; therefore, it is essential to prevent weeds from growing around your plants. You can apply a pre-emergent herbicide in the spring and fall to keep weed seeds from germinating. Hand pull weeds that are actively growing around your plant. Tomato plants can be sensitive to herbicides, to ensure their health avoid using herbicide.
  
  

Treatment

• Apply a fungicide to your tomato plants. You can use a herbicide that contains chlorothalonil. Spray the plants with fungicide when their foliage is dry or in the morning. Use the fungicide every seven to 10 days. Prune off damaged leaves with a pair of bypass shears. If the disease becomes a yearly problem, rotate your tomato crop to get them out of the area. Unfortunately, there are no septoria leaf spot resistant tomato plants available.