Why do tomato plant leaves turn yellow?

When plants do not receive adequate water, then the yellowing of the leaves on the bottom of the plant can be observed. Other reasons for the occurrence of yellow leaves on the plant are lack of nitrogen in the soil and curly top virus.

The problem can be controlled by deep watering the plants during hot weather conditions, adding compost or transplant mix to the soil, supplying adequate quantities of nitrogen to the soil and protecting the plants from pests.