what causes tomato leaves to yellow and die off
Lower leaves turn yellow & then brown off. Some flowers set but plant eventually dies!
First step is to check your cultivation practices - problems most often are caused by improper watering, soil management, or fertilizing. Check the guidelines in this article: https://www.gardeningknowhow.com/edible/vegetables/tomato/yellow-tomato-leaves.htm
After this, check for insects and disease. https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-blossoms-no-tomatoes.htm
You can also call the nearest botanical garden for information about contacting a master gardener group, who will help you with analysis and treatment.