Cedar-Apple Rust

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Cedar-Apple Rust

You may be seeing orange gelatinous blobs with what looks like tentacles on redcedar or juniper trees now or soon as we get more warm wet weather. This is cedar-apple rust, which is a fungus and as the name suggests requires two hosts to complete its lifecycle, cedars and apples. Cedar-apple rust is typically a non-injurious disease on redcedar and juniper, however on apple, the pathogen can infect leaves and fruit of susceptible cultivars and may cause premature defoliation if infection is severe.

Life cycle

Redcedar/juniper, becomes infected by spores released from aecia on apple/crabapple in mid-summer. The pathogen then grows and begins to induce the formation of galls on the tree the following summer, which continue to grow throughout fall and winter. With rainfall increasing in early spring, the galls develop telial horns (the tentacles), which is the fruiting body that will produce spores that can be carried for several miles on the wind. Those spores that land on the alternate host, apple/crabapple, will develop into lesions on leaves or fruit which form small pustules on the upper side of the lesion surface. Eventually they will develop thick tube-like protrusions called aecia on the underside of the lesion. This fruiting body produces spores, which are released into the air and land on nearby redcedar/juniper around mid-summer causing the life cycle to repeat itself.

Cedar-apple rust on both hosts


Cedar-apple rust is a common disease that apple, crabapple, and ornamental plant producers, landscape managers, and property owners must constantly deal with across the United States. There are a few options for management of this pathogen. Like stated it is typically a non-injurious disease on redcedar and juniper so if you are not growing apples it’s more of a cosmetic issue for a few weeks of the year. For a cultural control method, you can remove all of one of the hosts, either all apple or all cedar trees, within a 5 mile radius. This is not very practical and a better option is to use cultivars such as Red Delicious, Gala Supreme, McIntosh, and Liberty that are considered resistant to cedar apple rust. Lastly there are fungicides that can be used and are typically applied on a 7 to 14 day interval.