Christmas In July: Some hawthorns these past two weeks are sporting little orange sherbet-colored aecial spore masses of the cedar quince rust fungus (Gymnosporangium clavipes), pushing out from the haws. I am receiving many calls about this and, Frits Rizor, the Executive Director of the Ohio Nursery and Landscape Association, even sent me a text and image the other day – we are all plant pathologists!
Colorful and attractive Christmas ornaments on the tree, except. Except for our realization that the millions of spores from these fruits might be tracked into a customer’s house. Except for us knowing that apple growers (apples are also a host for this fungus) must spray in the spring to keep this fungus off the fruits which otherwise we would not buy. Except if we are nurserymen who need to protect their specialty junipers from being infected by this fungus and potentially ruining their crop a year and a half later. Except if you are a landscaper who has a hawthorn turn from an ornamental asset to a liability as affected twigs die and make the tree unsightly.
This fungus takes a wild almost two-year ride, back and forth between junipers (eastern red cedar) and plants in the rose family such as apple, hawthorn, and quince (rosaceous hosts). Unlike its cousins, Gymnosporangium juniper-virginianae that causes cedar apple rust and Gymnosporangium globosum that causes cedar hawthorn rust, the cedar quince rust fungus does not typically cause orange to reddish orange lesions on the upper leaf surfaces and aecial pustules on lower leaf surfaces of the rosaceous host leaves. Rather G, clavipes has masses of aeciospores emerge from the fruits and from cankered areas on stems of their host plant.
What to do now? It is too late to spray to prevent infection of hawthorns by fungal spores arriving from junipers in spring. The spores on the hawthorns now will not re-infect the rosaceous hosts, so sprays on the hawthorns now are beside the point. Most will not want to spray junipers to stop infections from spores arriving from the hawthorns in coming months, but that nurseryman might: disease is in the eye of the beholder in terms of how important this problem is to a particular horticulturist. You can decide not to plant junipers near rosaceous hosts. And…you can learn more about cedar quince rust and diseases, about insect and mite problems, about the best horticultural practices and about new and trusted plants…at all the fall and winter and then spring programs available to the green industry and other plant lovers.
So, to reinforce this message about cedar quince rust and about educational opportunity, and to highlight the Ohio Turfgrass Foundation’s Brian Laurent and his video stylings, check out this video about cedar quince rust near Powell, Ohio and the OTF Conference and Show & The Ohio State University Green Industry Short Course on December 5-8, 2016. Check it out at:
Now that you have watched the video - here is one last bonus. While Brian and I were taping and I was taking pictures of the hawthorn tree, I noted another biological phenomenon: woolly apple aphids (Eriosoma lanigerum), which spend part of their life on the rosaceous plant roots, now sucking sap from stems of these hawthorns, then after they had their fill, their excretions were used by ants that farm the aphids. Nature, man oh man.