White pine blister rust is a deadly rust fungus that affects the stems of five-needle pines, or “white pines.” It is a non-native disease that is believed to have originated in Asia and was introduced to the United States from Europe in the early 1900s. There are five susceptible species of five-needle pines in the United States, including the whitebark pine.

Blister rust has a complex life history that includes alternate host plants such as currants, gooseberries and mallow, which are key components of infection transmission to pine trees. Fungal spores grow on alternate plants and are then released into the air and adhere to pine trees, which can infect and kill the whitebark pine from seedling to mature tree.

When the disease was discovered in the 1930s, several western national parks attempted to control it by removing the alternative host plants. This campaign was designed to save the pines at the expense of other native species and resulted in the destruction of countless native plants, the spraying of over half a million gallons of the herbicide 2-4-5T in national parks, and the deployment of massive work crews over four decades. In 1971, the campaign was deemed ineffective and abandoned.

Current research is focused on identifying rust-resistant trees for seed harvest and replanting to create stands that have natural immunity or reduced susceptibility to blister rust. Collecting seed from “plus trees” – trees that appear to be free of rust – and further testing in the nursery to identify “elite trees” – trees that are proven to be rust-resistant – is a long and expensive process. To streamline the process, some parks are studying the effectiveness of no-till – sowing seeds directly into the soil versus allowing them to grow as seedlings for 2-3 years. Further research into the genetic makeup of elite trees is underway and could shorten the process of identifying rust-resistant trees using faster methods such as needle-probe testing.