What is wrong with my tomatoes and squash?

What is wrong with my tomatoes? They are starting to make tomatoes, but some of the leaves are turning yellow. The usual cause of that problem is water-either too much or not enough water will produce the same symptom. Are you sure that you are watering the plants enough in this dry summer? If so, think about the idea that the tomato plants are too wet. Before you water them, check the soil. Do not turn on the irrigation system until the top inch of dirt is dry. Roots need water to stay healthy, but they also need air. If the air spaces in the soil are full of water, the roots begin to drown....