Cedar Apple Rust

by Sherrie Smith and Jason Pavel

Juniper Cedar Apple Rust Telial horns – Gymnosporangium juniperi- virginianae

Photo by Rick Cartwright, University of Arkansas Cooperative Extension

Days of rain have made ideal conditions for rust diseases. Many species of rust attack pear and apple trees. Most require juniper species as an alternate host. These rusts also attack hawthorn, quince, mountain ash, and other rosaceous species. Cedar Apple rust is the most economically important rust seen east of the Rocky Mountains. It can cause serious yield loss and almost total defoliation in susceptible cultivars.

Galls on cedar trees exude bright orange tentacles during wet weather in the spring. The tentacles, (telial horns), become swollen and jelly-like during rains and produce teliospores. Pears do not get Cedar Apple Rust but get rust from other species of Gymnosporangium. With all species of Gymnosporangium, teliospores produce basidiospores which infect nearby apples and other members of that family. Orange-brown lesions, pycnidia, appear on the upper side of pear or apple leaves a few weeks after infection. One to two months after the appearance of the lesions on the upper leaves, aecia develop on the underside. The spores from the aecia infect nearby cedars and junipers and begin the cycle over again.

The first symptoms are yellow to orange-red spots on the upper sides of the leaves and on fruit. Leaves 4-8 days old are the most susceptible, and fruit is the most susceptible from the tight cluster stage until just after petal fall. Fungicides such as Captan should be used at the pink bud stage on susceptible ornamental and fruit trees until 30 days after petal fall. Removal of wild cedars within a ½ to 1-mile radius of orchards breaks the cycle. Galls should be pruned out of landscape junipers during the dormant season. It is helpful to plant rust-resistant fruit trees.

Cedar Quince Rust on Pear – Gymnosporangium clavipes

Photo by Jennifer Caraway, University of Arkansas Cooperative Extension