Sunburn

• Too much exposure to sun and high heat will cause some young tomato plants to have white leaves. Control the sun and shade the tomato plants are exposed to in order to create a healthy temperature level.
  
  

Windburn

• Tomato plants in open, windy areas may show damage on their leaves in the form of whitening. Windburned leaves also feel dry and may curl from lack of moisture.
  
  

Leaf Miners

• Leaf miners are an insect larvae that leave squiggly white trails on tomato plant leaves. Look for pests on your tomato plants if the leaves are turning white. Pick off and destroy the affected leaves after you find and remove any leaf miners from the tomato plants.
  
  

Late Blight

• Tomato plants in cool, wet climates may develop gray spots surrounded by white mold, which is indicative of late blight. Any plants affected by blight should be removed and destroyed. New planting ground should be chosen for the following year's plants.
  
  

Hardening

• Hardening is a process of gradually introducing a newly grown seedling or plant to an outdoor environment. The time of exposure is slowly increased until the plant is prepared for life outside. Hardening tomato plants before they're planed outside can prevent many issues of sun and wind overexposure.