Blister rust is a non-native fungal disease that is lethal to white pines. The disease originated in Asia and has been rampant among pine trees in North America since the 1950’s. The fungus normally infects the lower part of the tree and is the only type of rust fungus that directly attacks the main bark of pine trees.
How White Pines Become Infected
In order for white pine trees to become infected with the disease, there must be one of several other species of trees nearby. Examples of such trees include gooseberry and currant trees, with some of these plants being more susceptible to the disease than others. These trees act as carriers for the white blister rust, and when the wind blows it transports the fungus spores from the diseased plants, spreading the fungal infection to vulnerable white pines.
What the Disease Looks Like
Symptoms of blister rust will only start to appear a year or two after the white pine has been exposed to infection from these plants. First, the infected branch will swell slightly and discolor, forming something called a canker. The needles on the diseased branch will then become infected too, and start to die. The needles will initially turn yellow, before turning orange, then even sometimes red. As the infection progresses, yellow or orange blisters may also form around the canker, and it will sometimes leak a clear or white sap. Once a branch on a white pine tree has been infected with blister rust, there is no way it can be saved.
How to Stop the Spread of Infection
If the other branches and main stem remain uninfected you can still save the remaining tree by cutting off the dead branches, which will stop the infection traveling upwards. To further avoid infection, it is best to extract diseased gooseberry and currant trees from areas surrounding existing white pines.
It is very unfortunate that white pine blister rust is so common, as the infection has detrimental effects on the rest of the environment too. White pines provide food and shelter for many wildlife animals such as white-tailed deer and songbirds, and when the trees become infected it lessens these creatures’ opportunities to access such necessities. Additionally, the natural beauty of forests and parks in New England attracts many millions of tourists every year, and fungus-infested white pines are not the most appealing.
But there is still hope. While it is unlikely that white pine blister rust will ever be eradicated, management and prevention techniques can be employed to try and ensure the prevalence of the white pine tree in the northeast.
Maloy, O. C. (2001). White Pine Blister Rust. Retrieved from plantmanagementnetwork.org: https://www.plantmanagementnetwork.org/pub/php/management/whitepine/
Munck, I.A., Tanguay, P., Weimer, J., Villani, S.M., Cox, K.D. (2015) Impact of White Pine Blister Rust on Resistant Cultivated Ribes and Neighboring Eastern White Pine in New Hampshire. Plant Dis. 99:1374-1382. doi:10.1094/PDIS-12-14-1338-RE
Rebecca Koetter, Michelle Grabowski. (2017). White Pine Blister Rust. Retrieved from umn.edu: http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/white-pine-blister-rust/
Department of Natural Resources. (2017). White Pine Planting and Care - Tending White Pine. Retrieved from dnr.state.mn.us: http://www.dnr.state.mn.us/treecare/whitepine/tending.htm
Eastern White Pine Branch Infected with White Pine Blister Rust: "Cronartium ribicola on a pine tree Pinus strobus (white pine blister rust)" by Marek Argent is licensed under CC BY-SA 3.0