What is Cedar Apple Rust?
Cedar apple rust is a fungal disease found in the Eastern region of North America caused by Gymnosporangium juniperivirginianae. This disease can affect a wide range of hosts across many species of cedar, apple, pear, and quince. There is a unique dependency for this disease to develop in hosts like cedar in order to eventually infect tree fruit crops. The presence of cedar apple rust can reduce the quality and aesthetic appearance of the fruit, often rendering it unfit for fresh market sale. With a large enough infection, the foliage of the leaves will be negatively affected and likely cause defoliation in the canopy.
What does Cedar Apple Rust look like?
Large light brown/tan galls can be seen on diseased branches of alternate hosts of cedar apple rust such as the Eastern red cedar in early spring. These galls require two years of development to reach the point of spore release and spread, so in the second year the galls will open into orange horn-like structures. During sporulation and spreading of fungal inoculum, the fungal structures look orange and gelatinous. Once the infection takes hold in the apple, cedar apple rust lesions appear as bright yellow-orange spots with a red ring around the edges of the lesion on the top side of the leaf. On the underside of the leaf, the spore-producing structure appears as a brown spot with raised black dots. When the young fruit gets infected orange spots form in a circular formation.
Where does Cedar Apple Rust come from?
Cedar apple rust develops primarily on several species of cedar (Juniperus). The most common US host of this disease is the Eastern red cedar (Juniperus virginiana). Cedar apple rust is dependent on this alternate host to develop and eventually spread to apples. Typically, the distance of spread from the original host to an alternative is approximately a mile or less.
How do I prevent and control Cedar Apple Rust?
– Choose a planting site that is distanced from a forest line
– Remove cedar trees in close proximity to the orchard
– Prune diseased branches of cedar trees less than a mile from the orchard
– Prune infected branches
– Plant disease resistant cultivars1
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