For Release May 7, 2006

My Orange Cedar Tree

AGRI-VIEWS
by Chuck Otte, Geary County Extension Agent

Every year we have a disease show up primarily in the native eastern red cedar, called Cedar Apple Rust. Every few years, for various reasons that I will explain, we have an exceptional case of it and the phone calls come in by the score. Unlike many plant diseases, you can see the effects of Cedar Apple Rust even while rolling down the highway at 60 MPH. As the disease reaches the end of it's 21 month life cycle on the cedar tree it produces a gall, that following a spring rain storm, rapidly grows long orange tendrils that will probably remind you of an alien jellyfish!

Let me walk you through the two year life cycle of this disease starting with where we are right now. Cedar Apple Rust is a rust disease that requires two hosts. The orange tendrils that are being seen on the cedars, with every rain, are producing spores that will land on the leaves of apples, flowering crabapples and other closely related species. High susceptible untreated trees will be nearly totally defoliated by this disease in coming weeks. While this disease will not actually kill either the cedars or the apples, it can be very devastating to the apple trees, reducing fruit production and decreasing the vigor of the tree making it more susceptible to other problems. If you haven't already done so, spraying your apple and flowering crabapple trees with Immunox once a week from now through early June would be very advisable.

The disease continues to live on the apple leaf throughout the summer. In late summer or early fall, when we have high humidity or rainfall, the leaf spots develop tiny little horns on the underside of the leaf. These horns release spores that will be moved by the wind back to the cedar trees. This period of infection can occur for two to three months in the fall. The disease spore colonizes the ends of a branch on the cedar tree and starts to grow slowly.

This newly developing gall is easily overlooked in the fall and early in the next year. It won't really be noticeable until the end of the summer following the fall infection. At this time it can be anywhere from ¼ inch up to one inch in diameter. It will be greenish to brown in color and have a corky appearance, especially if it is broken apart. As we move into the second spring on the cedar tree the gall matures and starts to project little stiff hair like structures out of the gall. When the weather warms up and we start to have rain showers, these tendrils, called telia by the plant pathologists, will start to grow rapidly, become gelatinous and orangish in color. While they look rather slimy, they are more silky smooth to the touch.

For a heavy occurrence of these galls in the spring we need two things to have happened. We needed a good fall infection period 21 months ago and we need warm moist rains this spring. We apparently had both of those conditions. The galls will stay active for several weeks, until early June. At that time the galls shrivel up and die so that they'll look like little black nubbins. These will stay on the tree for a year or more eventually falling off.

While the disease is very unsightly on the cedars, it really does very little damage to the cedar trees. Occasionally a branch tip may die but that's about it. Since the fall infection period is so long and the foliage is so dense on a cedar, treating the cedars is quite impractical. But, we do need to focus on treating the apple trees. Ideally we start spraying the fungicide before the first galls appear, but I would still treat with a thorough spraying of Immunox repeating weekly through early June.

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