Don't plant tomatoes too early in the season, or use plastic mulch to warm the soil. Once soil temperatures rise, the problem usually corrects itself. Curly top virus is transmitted by the beet leafhopper. This problem is common in western Colorado but seldom found in eastern Colorado. Infected plants turn yellow and stop growing.
Upper leaflets roll and develop a purplish color, especially along the veins.
It is difficult to control because leafhoppers migrate from southern areas. Hot, dry springs with predominantly southwest winds usually indicate increased problems with this disease. No chemical controls are effective. Use row covers to protect tomato plants from the leafhopper. Stems may become distorted, giving the bush a zig-zag appearance.