Types

• Fusarium crown rot causes tomato leaves to turn black or brown and wilt or even fall off. Blight and septoria leaf spot also cause rotting spots on tomato leaves. Blight spots have rings of tan coloring, while septoria spots are gray with black specks.
  
  

Effects

• Minor leaf rot diseases look unattractive. As fungal leaf rots progress, they can cause leaves to wilt and even fall off. Since tomato plants need leaves for photosynthesis, defoliation can kill the plants.
  
  

Prevention/Solution

• Gardeners should purchase healthy tomato plants from reputable nurseries and avoid watering them by spraying their leaves. Colorado State University Extension suggests removing infected plants and planting in a new area the following year to prevent fungi from spreading, especially for cases of fusarium crown wilt. The University of New Hampshire Cooperative Extension suggests chlorothalonil fungicide for blight and septoria.