When available, it is also helpful to use resistant varieties. Chemical controls are not effective for these fungi. Rusts, Coleosporium, Puccinia, Uromyces. Symptoms of rust infection are first visible as chlorotic lesions on the upper leaf surface. Diagnostic symptoms then develop on the underside of the leaf and appear as pustules which break open to reveal the orange-rusty powdery spores for which these diseases get their name.
Rusts can result in some defoliation, especially when plants are crowded.
These diseases can be minimized by cleaning up plant refuse in the fall and by adequate spacing of the plants to promote good air circulation. Although not usually necessary, applications of fungicides can be made when new growth emerges in the spring. Among the compounds registered for use in Connecticut are mancozeb, maneb, and triadimefon. Consult the label for dosage rates and safety precautions. Botrytis blight, Botrytis cinerea.