Q.Growing Tomatoes Near Pecan Trees

I have just planted eight tomato plants that I started from seed inside in early February. The weather has been consistently in the 70s and 80s since I planted, and nighttime temps have not been below 40. The leaves on the plants have turned yellow with white right at the edges, and the plants seem to have stopped growing. I’ve heard that walnut trees can kill tomatoes, and I have pecan trees all around the garden. Could this be the problem?