My opinion, which is not professional, but slightly experienced, if the leaves that are yellowing are the lowest leaves you don't have much of a problem. Cut the branches off. You want to create a good distance between the lowest tomato leaves and the ground...having lower branches of the tomato plant hanging too close to the ground, touching the ground, or having dirt splashing onto your lower leaves is something you want to avoid happening. Having them too close to the ground or dirt splashing onto them when it rains may cause problems such as blight or transmission of other disease. Anyway, it just looks like the plant is doing its job of getting rid of leaves that have been depleted of their necessity and/or neutrients. Again if it is just lower leaves, ditch the leaves or the whole branches. If you're getting a lot of rain and concerned about early blight, grab a copper fungicide from a lawn and garden store to spray after rainy periods and every 1-2 weeks.

Thank you. That makes sense. I will remove the lower leaves.

Thank you. That makes sense. I will remove the lower leaves.