The front of the seed packet indicates whether the variety is resistant to specific diseases. Root-knot nematodes cause galls, or knots, on tomato roots. Early blight is evident on the leaves.
Late blight affects the fruit.
Plant specialist Dr. Alan Windham explains how to cope with tomato diseases. The best way to prevent them is to choose resistant varieties. If you see the initials VFN on a tomato seed packet, it means that the variety is resistant to verticillium wilt, fusarium wilt and root knot nematodes. A T on the label means the variety is resistant to tobacco mosaic virus, which can be problem for tomatoes, especially if they're grown near tobacco. Infected plants usually have poor color and are unproductive.