Nikki-Thanks for your answer. I have been growing tomatoes for about 40 years, and I frequently see lower leaves turning yellow. I've never seen upper leaves turning bright yellow starting at the junction of the stem and the leaf. This looks a lot different from alternaria alternata or early blight. Even the small suckers have the yellowing. Any suggestions or help would be much appreciated.
Yellow Upper Leaves on Tomatoes
Certified GKH Gardening Expert
Well, this one has me stumped as well, though I did poke around a bit through all my books and such...I did find one possibility: "Tomato yellow top (TYT), a destructive disease of tomato caused by tomato yellow top virus (TYTV). Terminal growth of infected plants is characteristically bright yellow, often with a purplish cast on lower leaf surfaces. Leaflets are ovate, cupped upward with constricted margins, and reduced in size. Blossoms often die and abscise and fruits are frequently asymmetrical."--Usually transmitted through green aphids. Neem oil may help with that.
Not sure if it fits your circumstance or not, but nothing else I've seen seems to fit your description. Sorry, I couldn't be more helpful.