What causes tomato plants to get branches and leaves to have brown spots
The stems and leaves have small brown spots, then the leaves turn yellow, and shrivel up and the plants are dying.
Certified GKH Gardening Expert
Unfortunately, it sounds like early blight. This article will have more information: https://www.gardeningknowhow.com/edible/vegetables/tomato/early-blight-alternaria-tomato-leaf-spots-yellow-leaves.htm