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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Tuesday - July 17, 2007

From: Pensacola, FL
Region: Southeast
Topic: Diseases and Disorders, Trees
Title: Juniper as host of cedar-apple rust
Answered by: Nan Hampton

QUESTION:

Thanks for the helpful advice on the Eastern Red Cedar. I was wondering if you could ease my mind about a potential problem. I have read up on some of the native plants in my area in a very good book " Florida's Best Native Landscape Plants" by Gil Nelson. In it, the author advises to not plant the Juniper (Red Cedar) near crabapple or haws (because the Juniper is a host of cedar-apple rust). I recently planted about a month ago 'Crataegus flava', or summer haw, in my front yard (the same area I want to plant my Red Cedar). My question is, what is cedar apple rust, and how close is too close to plant a red cedar in relation to my summer haw? Is there any precautionary measures that can be taken to prevent the cedar apple rust from occuring? If I moved my summerhaw to the backyard and planted the red cedar in the front yard, could this prevent the cedar apple rust? I am open to any of your suggestions. Thanks again for your helpful advice.

ANSWER:

Cedar apple rust, cedar hawthorn rust and cedar quince rust are fungal infections that require two hosts—a Juniperus sp. (e.g., Juniperus virginiana (eastern redcedar)) host and a host in the Family Rosaceae (hawthorns, apples, quinces). On the junipers the rust forms galls that contain spores that are then transfered, mainly by wind, to the rosaceous species. Junipers are not severely impacted by the fungus. They will have galls and some twig death may occur but the effect is mild. On the hawthorns, apples or quinces, however, the spores have a more deleterious effect. Spots form on the leaves that may brown and die and fruit may be severely infected.

The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) says a distance of several hundred yards between the trees of the two species may offer protection. Ohio State University's suggestions for controlling the fungus include removing the galls from the junipers before they have time to ripen and spread their spores.

Mr. Smarty Plants would recommend that you move your summer haw to your backyard so that it is not in close proximity to your juniper. Then, watch your juniper for signs of galls and remove them as soon as they are found. This should offer protection against your summer haw getting the fungus.

 

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