Received to e-mails today from folks wanting to know what they can do about quince rust on mayhaws. At this point, since the disease is already expressing symptoms, there’s not much that can be done. The spores that are produced on the mayhaw will only infect red cedars (or maybe junipers), but not other mayhaws. The time to spray for this is beginning mid to late bloom and continuing through fruit development. Most commercial growers use a fungicide containing the active ingredient myclobutanil sold as Rally (formerly Nova). For homeowners, the fungicide Spectracide Immunox Multi-purpose Fungicide contains the same active ingredient and is labeled for use on a number of fruit trees. Unfortunately, mayhaws are not listed on the label.
Donald M. Ferrin, Ph.D., Louisiana State University Agricultural Center, Baton Rouge, LA