How to Identify Tomato Plant Diseases


Tomato plants can get a number of diseases that affect the health of their leaves and fruit. You can prevent some diseases, such as the tobacco mosaic virus, by not allowing tobacco to be used near your plants. You can treat other diseases, such as certain types of wilt and blight, by spraying or treating your plant with home remedies as well as chemicals. You must first learn to identify tomato diseases before you can apply a cure.

Step 1

Look for black or brown circular spots on the lower leaves of your tomato plant. They could indicate a fungal disease called tomato blight. In the later stages of this disease, leaves will die and fall to the ground and fruit will rot on the vine. Mississippi State University Extension suggests spraying blighted plants with 4 parts copper sulfate, 4 parts lime and 50 parts water.

Step 2

Water your tomato plant if it begins to wilt. If watering does not improve its condition, it could have either Fusarium or Verticillium wilt. Both of these fungal diseases commonly enter tomato plants through their roots, then move up into the plant's tissues and prevent water from reaching the leaves. Planting tomato cultivars that have been bred to be resistant to these diseases is the best way to prevent them from occurring.

Step 3

Monitor your tomato plant for leaves that develop a mosaic-like pattern. This condition might indicate the common disease called tobacco mosaic virus. It manifests itself as patches of light green or yellow on the leaves, mixed in with patches of normally colored leaves. It can also affect flowers and fruit and cause stunting of the entire plant. Although tobacco mosaic virus does not often kill a tomato plant, it can seriously affect its ability to produce a good number of quality fruits.

Step 4

Watch for stunted growth of your tomato plant and leaves that curl up and appear puckered. These are symptoms of the tomato leaf curl virus that occurs when whiteflies attack your plant. Controlling this insect by hanging yellow sticky traps around your plant can help. Some varieties of tomatoes are bred to resist this virus.

Step 5

Examine your plant from time to time to determine if it is developing dark spots on its leaves and stems. As the tomato spotted wilt virus progresses, cankers also form. Fruit will develop yellow spots or rings that appear as a mosaic pattern. Thrips cause this disease and both the insect and the disease are very hard to control, according to Colorado State University Extension. Uproot and destroy any plants that are infected.

Things You'll Need

  • Powdered copper sulfate
  • Hydrated lime
  • Sprayer
  • Sticky traps


  • Mississippi State University Extension: Plant Pathology Infobytes
  • University of Minnesota Extension: Tomato-Tobacco Mosaic Virus Disease
  • Texas A&M University Extension: Tomato, Part I
  • Colorado State University Extension: Common Tomato Problems
  • AVRDC International Cooperators' Fact Sheet: Tomato Diseases
Keywords: tomato plants, fungal virus, diseases garden

About this Author

Barbara Fahs lives on Hawaii island, where she has created Hi'iaka's Healing Herb Garden. Fahs wrote "Super Simple Guide to Creating Hawaiian Gardens," and has been a professional writer since 1984. She contributes to Big Island Weekly, Ke Ola magazine, GardenGuides and eHow. She earned her B.A. at UCSB and her M.A. from San Jose State University.