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What is growing on my cedar trees?
Clark MacCallister
If you have any cedar trees on your property, you may have recently noticed several bright orange, slimy balls growing from the branches. These growths are the fruiting bodies of a fungal disease called cedar-apple rust, known to scientists as Gymnosporangium juniper-virginianae. Cedar-apple rust is one of the most fascinating fungal diseases we encounter. It is interesting because it requires two host plant species, cedar and apple, to fully complete its life cycle each year. This fungus survives through the winter on cedar trees, having been infected the previous year. Fungal spores from infected apple trees travel to cedar trees by wind and animal movement and infect cedar needles and buds. Small, almost undetectable growths develop on the cedar branches, which enlarge in the spring during moist weather. These galls swell and produce orange jelly-like growths called telial horns. During a very wet spring, like what we are experiencing in 2018, these billiard ball-size galls can seem to cover up cedar trees.