Photographer: Susan K. Hagle Affiliation: USDA Forest Service Source: www.bugwood.org Copyright: CC BY-NC 3.0
White pine blister rust (Cronartium ribicola) is a fungus found in cool weather climates that can be described by cankers that appear rust-like in color. This fungus is able to choke tree branches by surrounding the branch with a canker that prevents nutrient travel in the phloem and xylem just below the bark of the host tree.
Symptoms: The initial symptoms of white pine blister rust are difficult to notice in the form of small red or yellow spots on branches or pine needles. Within the first year of infection cankers can be found on branches appearing as slightly yellow swollen areas. Distant symptoms can be recognized as dying branches or trees with stunted growth.
Host(s): Members of the genus Pinus which can be described as pine trees with 5 needles per bundle. The most common hosts in North America are Pinus strobus (eastern white pine), P. monticola (western white pine), P. lambertiana (sugar pine), P. albicaulis (whitebark pine), P. flexilis (limber pine) and P. strobiformis (southwestern white pine).
White pine blister rust has been described by several sources as the most destructive disease of trees in North America. White pine blister rust is a fungus that thrives in dark cool areas, which allows several pine trees to be prime hosts. The fungus has spread throughout the majority of native regions for pine trees between the late 1800's and 1950 causing severe damage and eventual death to many native pine tree species.
The life cycle of white pine blister rust is very complex and requires favorable environmental conditions to reproduce viably. Infections of this fungus are not consistent from year to year due to dynamic weather conditions preventing dispersal length of the spores, which can be as little as 300 m.
This fungus does not spread directly from tree to tree. Introduction of white pine blister rust occurred through a shipment of contaminated seedlings that most likely showed no symptoms of the disease. The seedlings were believed to have been received in 1910 to the United States from Europe.
U.S. Habitat: White pine blister rust is most common in cold or moist areas that provide favorable conditions for reproduction of the fungus spores. Areas of higher infection on the host plant are typically closer to the ground where needles are moist for long periods of time.
There is not a management method proven to completely eradicate white pine blister rust, but there are some methods that are able to control small outbreaks if caught early on host plants. Some forest officials recommend pruning host trees that have isolated small outbreaks and quarantine of plants located in a small area with the infection. Methods of genetic resistance are currently being developed to help establish a natural defense for North American Pine trees most at risk for the fungus.
Schnepf, C. 1997-98. White pine blister rust: Pruning can increase survival. Univ. Idaho Coop. Ext. Woodland Notes 9:2.
Woodward, Susan L., and Joyce Ann. Quinn. 2011. White Pine Blister Rust. Encyclopedia of Invasive Species: From Africanized Honey Bees to Zebra Mussels. Santa Barbara, CA: Greenwood. 29-35. Print.