White pine blister rust: what the agencies record

This page reports what the official source says. It is not legal advice: ask the office named here. It is not a diagnosis of any tree and does not say what should be done with one. White pine blister rust is caused by the fungus Cronartium ribicola. Each section names its source, all read on October 9, 2026. The full list of diseases is on the tree diseases page.

Origin and importance

Natural Resources Canada, called NRCan, says the disease was introduced from Europe at the turn of the 20th century and is economically one of the most important forest diseases in North America. It says the rust reduced reforestation of white pine in Quebec despite the species' commercial value, and that in many regions of Canada the volume of white pine has been depleted so far that the species is not seen as commercially viable. The Maine Department of Agriculture, Conservation and Forestry, called Maine DACF, says the fungus was introduced into the United States around 1900 and has since spread throughout the range of white pine, causing mortality and severely reducing the commercial value of eastern white pine. NRCan calls it the only stem rust of white pine, which sets it apart from other Cronartium rusts by host.

Two hosts

Host	What the sources record
Five-needle pines	NRCan lists eastern white pine, limber pine, western white pine and whitebark pine as main hosts. Maine DACF names eastern white pine. The Pacific Northwest handbook calls white or five-needled pine the alternate host and says rust of white pine has caused severe losses
Currants and gooseberries (Ribes)	NRCan says the fungus alternates between five-needle pines and Ribes, and Maine DACF says it cannot spread from pine to pine and needs Ribes to complete the cycle. The handbook says black currant is more susceptible than red currant, that the red currant cultivars Viking and Red Dutch are practically immune, and that some wild Ribes species are very susceptible

Life cycle as the sources state it

NRCan says infection of pine takes place through the needles in the fall. The fungus grows through the phloem and bark with no visible symptoms for at least three years before spores form. In the spring of the third or fourth year, white blisters break through the bark and release aeciospores, which can infect only Ribes. About 10 days after infection of a leaf, urediniospores start to develop on the leaves and continue through the summer, which can reinfect Ribes and intensify the disease there. In the fall, teliospores and basidiospores form on Ribes and carry the disease back to pine. The handbook agrees: wind spreads aeciospores from orange pustules on pine cankers to Ribes in spring, rain and long wet periods encourage infection on Ribes, brownish hair-like telia form in late summer, and basidiospores blown to white pine start new infections. It says pycnia then appear on the bark the following spring and aecia erupt from the same place the year after, producing spores every year until the branch dies.

Signs on pine

NRCan says many tiny yellow dots appear on the needles the spring after the fall infection. Over one to two years after that the fungus spreads to the branches and trunk. In mid-summer orange pustules form on the stem and exude a liquid carrying the first spores. The following spring white blisters form, and the canker keeps growing. Foliage above the canker yellows and turns reddish brown. NRCan says the dead upper part can break and give decay fungi a point of entry. Maine DACF describes cankers with large amounts of dried resin and a yellow-orange aecial stage, with spores visible for up to five weeks, and says the fungus can take a few years to girdle the stem and kill the tree. NRCan says basal stem cankers producing resin might be confused with Armillaria root rot, which is told apart by white mycelial fans under the bark.

Signs on Ribes

Maine DACF says symptoms on Ribes develop throughout the growing season and are comparatively mild: the lower leaf surface turns pale, and within days tiny orange pimple-like fruiting bodies, called uredinia, form. The handbook describes angular lesions with orange uredinia or black to brownish telia on the underside of the leaves, and says defoliation of infected plants is common as lesions increase.

Regulated status and reporting

Maine DACF says planting or possession of European black currant, Ribes nigrum, or its varieties or hybrids is prohibited anywhere in the State of Maine. It says the sale, transportation, planting or possession of other Ribes is prohibited in a list of counties: York, Cumberland, Androscoggin, Kennebec, Sagadahoc, Lincoln, Knox, Waldo and Hancock, and parts of Oxford, Franklin, Somerset, Piscataquis, Penobscot, Aroostook and Washington. The quarantine is administered by the Forest Health and Monitoring Division of the Maine Forest Service, phone (207) 287-2431 or (207) 287-2791. NRCan and the handbook name no quarantine. For other places, see the guides on reporting a pest in Canada and the United States. For the host tree, see eastern white pine.

Management as the sources list it

NRCan reports Canadian Forest Service research showing that pruning low branches, infected and uninfected, could reduce the rust in plantations where Ribes are absent or rare. The handbook describes distance between Ribes and white pine, and fungicides for currant growers. This page gives no spacing figures, product names or rates. For who may apply pesticides, see pesticide licences.