Problems on tomato leaves: light spots

by Celia
(Co. Mayo, Ireland)

Q. I see that you have that problem listed, but can you tell me what causes light spots and how I can help my plant? I'm growing my tomatoes in huge pots. Thanks in advance.

Tomato Dirt responds:
Light spots are common on tomato plants! You didn't mention any other symptoms or what your growing conditions have been like, but the spots on your tomato leaves could indicate a number of things:

• Sun scorch. Most often it's the fruit that's impacted by intense sunlight, called sunscald, leaving light-colored patches on tomatoes. But sun can scorch leaves, too, particularly if plants are just acclimating to the garden. Try to shade plants as they harden off and for the first few days you place them in the garden, particularly if the sun is bright.
  
• Septoria leaf spot. Lower tomato leaves show symptoms first, with round, yellow, or water-soaked areas that soon become dotted with dark spots. Spotting works its way up the plant. Septoria is caused by a fungus in the soil. It's most common in humid weather. Treat plant weekly with a biofungicide or a fungicide.
  
• Whiteflies, spider mites, or aphids. These pests are common on tomato plants both indoors and out. They cause leaves to yellow, get light spots, and leave a characteristic white sticky excrement called honeydew. Leaves appear shiny and are somewhat sticky when honeydew is present. Treat plants with an
  insecticidal soap
  or Neem oil.
  
• Leaf mold or powdery mildew. Both show characteristic light spots on tomato leaves. They're caused by a fungus. You can treat them with a biofungicide or a fungicide.
  
  Good luck and happy gardening!
  Your friends at Tomato Dirt