I'm surprised they have lasted this long. Snaps are a cool season annual in my area (almost a straight line east of Dallas). I plant them with pansies in the fall, and then pull them up and discard them when the heat moves in. Mine have been pretty for several weeks now, but will probably come out inside of two weeks more, if not sooner. The yellowing and brown spots are what I see when they begin to burn up in the late spring/early summer heat. Be happy! Pull them up and plant zinnias! :)

Puccinia antirrhini - aka snapdragon rust - a common malady, especially when temps are cool.

Some sulfur sprays are effective at prevention and help with control.

Al

donnabaskets, I must not have explained very well. The brown spots are only on the bottom of the leaves and the stems, and they are actually bumps. When I rub them I have a brown powdery substance on them. All of the brown spots are almost perfect circles. It is definitely not burn from heat as I have seen that on many other plants before. These same plants have made it through 2 previous summers here in Dallas. I don't know why. I know they aren't supposed to, but they have with no trouble at all from the heat. They are under a tree so that probably helps. I don't want to pull them up because I was happy I had found a plant that would live all year long. I spend so much money on plants that it helps to find some that last forever. They don't bloom all year of course (only in the spring), but they live and look good as little bushes. I don't even have to do anything to protect them in the winter and they are on the north side of my house! If you have any other thoughts on what this might be please let me know. I would really like to save them.

tapla suggested one problem above. I'm sure you and I both know how common fungal diseases are in our hot, humid (or cold, damp) south. Try tapla's remedy. If they recover, and you ever get seeds from them, let me know! :)