There are many reasons why leaves may turn yellow. This usually indicates that the tomato plant is under distress and is asking for attention.
Below are a list of reason that the leaves on your tomato plant leaves might turn yellow
- Your plants may have fusarium wilt or verticillium wilt.
- Your tomato may have Foliar leaf damage which is caused by a viruses and bacteria. Some signs that this was caused by bacteria/viruses is that you will see small dark spots on the yellow parts of the leaves.
- Damage caused by insects such as aphids or spider mites.
A Spider Mite
- Nutrient problems
- Tobacco mosaic virus
- The your tomato plants leaves are too wet
- The your tomato plants leaves are too dry