Cedar apple rust
Amy Jordan
Thursday, April 30, 2009
Its not Christmas time, but many trees around Lyon county seem to be decorated.
Our native evergreen, the Eastern Red Cedar (a juniper, actually), is adorned with orange balls after the many rains we have been receiving lately. These fungal galls are brown, brain-like structures most of the year, but now they are wild with bright orange gelatinous horns. Spores are released from the galls that infect apple and crabapple trees, as well as hawthorn and quince, which are the alternate host for the disease. The junipers typically are not damaged, but defoliation can occur on the alternate hosts.
To manage the disease, here are some options:
Resistance: For new plantings of fruiting or flowering apples, consider planting a rust-resistant variety.
Tree care: For any apple tree, proper pruning will allow air movement through the canopy. This practice reduces the leaf wetness that promotes disease. Maintaining overall tree health will also help prevent the disease.
Fungicides: Homeowners with a bad history of this disease (severe defoliation) might consider preventative fungicide sprays on the apple hosts when leaves are out and the orange galls are active. For best control, applications should continue through May or as long as the orange galls are active.
Products with the active ingredients myclobutanil or propiconazole are examples of materials labeled for cedar apple rust management in flowering crabapples and non-fruiting apples. Some myclobutanil products are labeled for fruiting apples. But in all cases, check the label carefully. For example, the myclobutanil product Immunox Plus is labeled for rust on flowering crabapples, but not for fruiting/eating apples because it contains an insecticide along with the myclobutanil ingredient. In contrast, Immunox Multi-Purpose Fungicide is labeled for fruiting apples.
The galls have been active for approximately two weeks, so some infection may have already occurred on the apple hosts, but future infections can be prevented with a fungicide application now.
Keep in mind the “disease triangle” when managing plant diseases. A host, pathogen and environment must be present in order for a disease to occur. For example, a host and pathogen might be present, but if the environment (or weather conditions) isn’t right, a disease won’t occur. Sometimes we have no control over the environment, but there are many things we can do to prevent disease, such as promoting good air flow so foliage doesn’t stay wet, avoid watering at night to prevent wet foliage, sanitation to prevent the spread of disease organisms, and planting resistant cultivars and plants that are adapted to our environment.
• Amy Jordan is a horticulturist with K-State Research and Extension in Lyon County.