Tree Diseases: Cedar-Quince Rust
Cedar-quince rust is a fungal disease that infects most varieties of eastern red cedar, as well as many other junipers, and alternative hosts. The disease is caused by the pathogen Gynosporangium clavipes. Cedar-quince rust requires two hosts to complete its disease cycle: an evergreen plant, and a deciduous plant. Infected plants generally experience significant branch dieback. Successive years of infection will reduce plant vigor. Some plant may eventually succumb to infection.
Distribution & Habitat
Cedar-quince rust occurs globally, wherever susceptible plants are present.
Cedar-quince rust infects a broad range of plants in the rose family. Quince and flowering quince are two of the most ideal hosts for the pathogen. Apple, crabapple, hawthorn, pear, chokeberry, photinia, and serviceberry are also frequently infected. Eastern red cedar, common juniper, prostrate juniper, Rocky Mountain juniper, and savin juniper are common evergreen hosts.
The disease pathogen overwinters in swellings that have formed on infected evergreens. In spring, when conditions become sufficiently moist, basidiospores are released from the swellings. The basidiospores are dispersed by air currents or splashes of rain to quince and other deciduous hosts, where they initiate new infections. After seven to ten days, spots or swellings begin to develop on the infected branches. In four to seven weeks, aecia form on the spots or swellings. Aeciospores are released from the aecia during rainy periods in late summer and fall. The aeciospores are disseminated by the wind or rain to susceptible evergreens, which they rapidly infect. Swellings form on the infected evergreens, and overwinter, beginning the cycle anew. In contrast to many other rust diseases, the swellings produced by cedar-quince rust may remain infectious for years.
Symptoms on Evergreens
Perennial, elongated branch swellings form on the tips of infected twigs and branches. As the disease progresses, the swellings may crack, and form cankers. Damp spring conditions cause orange, gelatinous blisters to erupt through the swellings. Small twigs and branches are often girdled, and killed. Severely infected evergreens may develop cankers on the main trunk. The girdling caused by the canker often culminates in plant mortality.
Symptoms on Deciduous Trees
On deciduous trees, the most conspicuous symptom of infection is the pink aecia that forms on the branches and fruit. Infected trees will often become laden with aecia. Perennial cankers develop on infected branches, and expand with each growing season. Most infected branches are girdled, and die back. Infected trees are often weakened, which reduces plant vigor. Cankers that extend into the main trunk may girdle, and kill the affected tree.
- When planting, select trees that exhibit an increased resistance to cedar-quince rust. Avoid planting junipers close to susceptible trees.
- Promptly remove and dispose of any infected twigs, leaves, and fruit. Avoid composting the diseased trimmings.
- Cull plants that have formed cankers on the main trunk. Diseased plants with cankers on the main trunk are hazardous, and may collapse easily, especially when subjected to additional stressors. Removing the affected plant will also limit or prevent the spread of the fungus to nearby trees and shrubs.
- Fungicidal applications may be performed on the twigs and branches of infected junipers. Initial applications should take place as soon as the orange, gelatinous blisters become apparent on the infected branches. Continue treating infected trees at two to three week intervals until the blisters become inactive.
Photo used under Creative Commons CC-by-2.0