   Comandra Blister Rust - May 2, 2001 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Rust fungi are complex and interesting plant diseases. About 7,000 species are known Some rust species grow and reproduce on one species of host plant while others require two separate plant species to complete their life cycle. The most common rust species are those that affect grain crops such as wheat, oats, and rye. In addition, they are difficult to control. One rust species of local significance is called Comandra blister rust (Cronartium comandrae). Comandra blister rust is a native disease that would normally be limited to young Ponderosa pine trees. On this native pine it is rare and fairly insignificant. However, the introduction of Mondell pine has provided a highly susceptible host for this disease. Mondell pine (Pinus elderica) goes by many common names including Quetta pine, Goldwater pine, Elderica pine, and Afghanistan pine. Infected trees usually are noticed when whole branches begin to fade and die during the summer months. This is a shame because Mondell pine is fast-growing, very drought tolerant, and is an excellent choice in desert and mid-elevation areas where Comandra blister rust is not endemic. This disease is common in Payson, Prescott, and Sedona. Comandra blister rust is a heteroecious rust: meaning that it needs two different host plants to survive and reproduce. Ponderosa or Mondell pines being a host for one portion of the rust's life cycle and bastard toadflax or comandra (Comandra umbellata) being the alternate host. The comandra plant is an herbaceous perennial that is usually found in areas with dense oak brush. Interestingly, the comandra plant itself is a parasite of other plants. It is thought that its primary host in our area is scrub oak (Quercus turbinella). The life cycle of Comandra blister rust alternates between pine and comandra. From and infected pine tree, aeciospores are disseminated by wind to the comandra plant where they infect the leaves during the summer rainy season. These spores can travel many miles. The rust grows on the comandra plant forming urediniospores, which then cause a secondary infection in the comandra plant. These infections produce teliospores that are responsible for the infections on Mondell pine trees. The initial infection of pine trees occurs through the needles. The fungus then becomes established under the bark tissue and forms swollen areas that ooze amber colored droplets the first year (containing spermatia). The following year, blisters form on the bark which eventually burst releasing the bright orange spores that will, in turn, infect the comandra plant and set the cycle in motion again. No successful treatment for this disease is known. However, if infection sites are noticed, then the affected branches can be pruned out to prevent spread of the disease to the main trunk. The spores produced on pine trees cannot re-infect pine trees, so there is no immediate need to destroy the pruned branches. These spores can and will re-infect comandra plants therefore perpetuating the disease. It is my feeling that areas where Comandra blister rust is prevalent, native Ponderosa pines are harboring the disease and not really showing highly noticeable symptoms. The best advice is to not plant Mondell pine in Prescott, Payson, or Sedona. Most nurseries are aware of this disease and will not market Mondell pines to residents of these areas. Cottonwood, Camp Verde, and other areas of the Verde Valley appear to be safe from harm. If you have read this far, and were not turned of by my blatant use of biological terminology and botanical names, you may consider yourself a true science nerd. Normal people would have lost interest or turned the page by now. The University of Arizona Cooperative Extension has publications and information on Comandra blister rust and other plant diseases. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. Search past columns by keywords or send comments at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/. |