AboutJim Hyland Expertise I am an expert in Forestry, Forest Entomology, Forest Pest Control, and Forest Health. Extensive knowledge in Identification of insects and diseases of trees. Expert on Bark beetles and other insects that attack forests. Also a Registrated Forester with extensive knowledge in the management and care of forests.
Experience 34 years as State Pest Management Chief in a Southern state. Extensive knowledge in Forestry.
BS with major in Forest Management and Entomology Registered Forester Certified Pesticide Appicator
Question I have 2 Washington Hawthornes with swollen growths on most branches. These areas also are covered with orange "fingers" that are powdery (I noticed orange powder on leaves below this year). The swollen growths become black and hard. The thorns also get black swollen growths on them. I cut as many off as I could reach the 1st year. This is the 3rd year and the tree is so covered I'm afraid it's beyond help. I've been unable to identify the problem. At first I thought it was fireblight, but the symptoms don't match. Could it be some kind of rust? How is rust treated? I also have some cedar trees that get round growths on them and then turn black. The number in those 2 trees has also increased this year. Could these be related, ie, alternate hosts? I just read about this on a website, but am still not sure what this is and what I can do to help the trees.
Many thanks.
Answer Sounds like Hawthorne apple rust.
There are a number of "cedar rust" diseases in which the fungus completes its life cycle on two plant hosts; one in the cypress family and one in the rose family (the rosaceous host). Discussed here are three common cedar rust diseases in the northeast U.S.
Cedar apple rust (pathogen: Gymnosporangium juniperi-virginianae). The fungus alternates between Eastern red cedar (Juniperus virginiana) and mostly apple and crabapple.
Cedar hawthorn rust (pathogen: Gymnosporangium globosum). The fungus alternates between junipers and hawthorn, crabapple, and apple in addition to several other rosaceous hosts.
Cedar quince rust (pathogen: Gymnosporangium clavipes). The fungus alternates between junipers and a wide range of rosaceous hosts. The most noticeable in the landscape is hawthorn.
In some cases these diseases are minor problems, but cedar quince rust and cedar hawthorn rust can be a major problem on hawthorns and cedar apple rust is a major economic consideration in commercial apple production.
On apple and crabapple, bright orange-yellow leaf spots develop on upper surfaces of leaves in late spring , followed by light colored, fringed cup-shaped structures on lower leaf surfaces several weeks later. Damage on junipers is generally minor and involves presence of the galls and twig dieback. On apples and crabapples, fruit infections and leaf drop also can occur.
Cedar hawthorn rust: On junipers, galls are somewhat smaller than with cedar apple rust disease. Galls continue to produce spores on junipers for more than one year, compared to only one season of spore production with cedar apple rust. On hawthorn, leaf spots are similar to above and occasionally green twigs are deformed by the fungus.
Application of fungicides. Protective fungicides can be applied several times starting with prebloom on hawthorn and bud break on crabapples if the disease is chronically a problem at a given site. These applications are to protect the plant from spores being disseminated from the juniper host in mid-spring. Since there is no repeating cycle of this disease on the rosaceous host, further applications after this springtime spread from juniper are unnecessary. Commonly recommended fungicides include: Mancozeb (Fore, Dithane, Mancozeb); Chlorothalonil (Daconil*); Triadimefon (Bayleton, Strike) and propiconazole (Banner). It is the user's responsibility to follow all label instructions.
Sprays are rarely recommended to protect the juniper host from spores being disseminated from the rosaceous host in late summer and fall. One simple practice where only a few plants are involved is to remove galls from junipers.
