   Comandra Blister Rust - December 17, 2003 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Comandra blister rust is an endemic disease that affects ponderosa pine saplings. Mondell pine, a common Arizona landscape tree, is also very susceptible. Mondell pine (Pinus elderica) is a heat tolerant pine from the Middle East and is sometimes sold as a living Christmas tree. Mondell pine is also known as Quetta pine, Goldwater pine, Afghan pine, and Elderica pine. Comandra blister rust (Cronartium comandrae) is a very complex disease caused by a fungus. Like many other rust diseases, it requires two host plants to complete its life cycle. One stage of the disease is hosted by bastard toadflax (Comandra pallida). Bastard toadflax is a native usually found in growing in association with native Arizona oak species between 4,000 and 8,000 feet elevation. Spores formed on bastard toadflax can then be transported by wind to suitable host pine trees (ponderosa or Mondell). All observations of this disease indicate the spores are rarely transported further than one mile. The spores formed on toadflax-based rust colonies usually infect pine branches and trunks during spring or summer. When they land on a favorable location, the spore germinates and that pine tree becomes infected. The first season, swellings form on the pine and an orange liquid may ooze from the infection site. The second season, blisters form and bright orange spores are released from the infected pine tree during April or May. These spores cannot infect another pine tree. They will only infect bastard toadflax. The disease does little harm to the toadflax, but new spores are formed on toadflax the following year which can then infect susceptible pines. Thus the cycle goes-back and forth between the two host plants. As mentioned before, symptoms of infection on the pine tree are swollen branches and/or blisters that release orange spores. Following infection, the bark and underlying sapwood are colonized by the fungus causing infected areas to die back. Often, the first sign of Comandra blister rust is a dead branch in the middle of a healthy tree. Pruning out diseased wood seems to prolong the life of the tree, but once infected, the tree will eventually die from this disease. There are no known cures or treatments. High humidity and moisture favor Comandra blister rust. Irrigated landscapes are a perfect environment for the disease. We don’t know what makes Mondell pines so susceptible, but they appear to be the only introduced tree species that readily hosts Comandra blister rust. The disease has killed many Mondell pines in northern Arizona since their introduction. Unfortunately, the disease only became evident after significant numbers of them were planted and established in landscapes. Known hotspots in northern Arizona for Comandra blister rust are Sedona, Prescott, and Payson. Cottonwood and Camp Verde appear to be free of the disease. At the entrance to Dead Horse Ranch State Park, a big stand of Mondell pines (there they are labeled Quetta pines) was planted several years ago as a seed orchard. They appear to be free of the disease. A tree is a big investment in time and resources. If you live in one of the hotspots or have native oaks within one mile, avoid planting Mondell pines. Other species that you may want to consider are Austrian pine, pinyon pine, or another evergreen tree such as deodar cedar. For more information about Comandra blister rust (including photos), get the University of Arizona Cooperative Extension publication: Comandra Blister Rust available in local offices or on-line at: http://cals.arizona.edu/pubs/diseases/az1310.pdf. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/. |