Significance

• Early blight can cause leaves to yellow and fall away. The warm weather fungus also causes black spots on leaves and can affect stems and fruit. Defoliation may occur. Curly top virus causes the whole plant to turn yellow and stops growth.
  
  

Prevention/Solution

• Cucumber mosaic virus also affects tomatoes, causing the plants to yellow. Tomato plants must be removed and destroyed if infected, as the virus demonstrates an easy spread by incidental contact or touch.
  
  

Effects

• Bacterial canker and tomato pith necrosis often present with similar symptoms, including a yellowing of the stem and the yellowing and death of leaves. Fusarium wilt and Fusarium crown rot cause older leaves to yellow first, and the bottom half or one side of the plant may be affected while the other half appears fine. The wilt often causes drooping of the plant's leaves.
  
  

Warning

• The Colorado State University Extension warns that overwatering and root rot can also cause yellowing of leaves and symptoms appear similar to Fusarium infections. The extension recommends using proper crop rotation to avoid infection. Do not plant tomatoes, eggplant or potatoes in the same space for at least two years.
  
  

Considerations

• Whiteflies and aphid pests occasionally trigger leaf yellowing. Sticky honeydew present on the leaves indicates these pests may be present. The Colorado State University Extension recommends insecticidal soap to combat aphids if the damage becomes excessive.