Rose rust is a fungal disease caused by several species of Phragmidium. Symptoms can develop on leaves and any other green parts of the plant. Under favorable conditions, rust symptoms can appear on the entire plant. Small, orange pustules develop on both leaf surfaces in early spring. These gradually enlarge and become more pronounced on the lower surface of the leaf. Chlorotic or mottled areas can also develop on the upper surface of the leaf. These areas usually develop directly over the pustules on the lower surface. Young stems and sepals can also become infected. By late summer or early fall, the pustules turn black and contain the spores for winter survival. Heavy infections can result in premature defoliation. Foliage must be kept dry and diseased leaves removed from site. Pruning back diseased canes before winter is crucial. If these steps are observed, spray treatments can be quite effective.