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White pine blister rust

Rebecca Koetter and Michelle Grabowski

Importance

White pine blister rust (WPBR) is a devastating disease of five-needled pines and the only rust fungus that attacks the stems of white pine in North America. This disease can kill branches, upper shoots, creates stem cankers and can result in eventual death of a tree. White pine blister rust can be found throughout Minnesota but infection of white pine trees is most common in northern and eastern Minnesota where cool moist conditions in late summer favor infection.

Pathogen

The fungus Cronartium ribicola.

Susceptible plants

Eastern white pine (Pinus strobus) and other five-needle pines
Currants and gooseberries (Ribes spp.), indian paintbrush (Castilleja spp.), and lousewort (Pedicularis spp.)

Identification

Eastern white pine (Pinus strobus)

Ribes plants (Red, white and black currant, gooseberry)

Biology

The white pine blister rust fungus, Cronartium ribicola, needs to infect both white pine and a Ribes spp. to complete its lifecycle. Spores from infected Ribes spp. are carried to white pine trees on cool moist air currents in late summer or fall. These spores infect pine needles if moisture is present. The fungus kills the needle and moves into the shoot or branch, travelling about 3 inches a year as the infection progresses towards the main trunk.

Once the fungus reaches the branch, a canker is formed. The canker will girdle the branch and the infection will continue down into the main trunk. Seedlings and small trees are in great danger of dying from this disease when a canker girdles the main stem. Girdling stem cankers on older trees result in top-killing and the death of branches but this is usually not life-threatening.

In the first summer after infection of the pine tree, gummy orange droplets full of fungal spores may be seen on branch cankers. The second spring after infection, white blister-like structures form at the edge of the canker, these fungal structures, called aecia, crack open to release powdery yellow orange spores called aeciospores. These spores can be carried long distances on wind currents to infect Ribes spp.

Aeciospores infect the leaves of Ribes spp. causing yellow leaf spots and sometimes leaf loss. Just two weeks after infection, the white pine blister rust fungus creates a new type of spore, called a urediniospore on the lower surface of infected leaves. Urediniospores can only infect Ribes leaves and their production results in new leaf spots within the plant canopy and in neighboring plants. When days begin to shorten and temperatures drop, the white pine blister rust fungus produces short hair-like structures on the lower surface of infected Ribes leaves, called telia. Telia produce yet another type of spore, known as a basidiospore. Basidiospores are somewhat fragile and need cool moist air currents to carry them to nearby white pines. Basidiospores of white pine blister rust only infect five-needle pines.

Management

Resistant cultivars

'Paton's Silver Splendor' is a variety of eastern white pine that is resistant to White Pine Blister Rust. This variety was released by the University of Minnesota and has been available in nurseries for home landscapes since 2011. It is hardy to zone 3, distinctly upright and pyramidal when young. The tree has a silvery appearance, a fast growth rate and is 100 ft tall and 35 ft wide at maturity.

Many cultivars of gooseberry and currant with resistance to white pine blister rust are now available (Table 1). Resistance may be complete and no symptoms of disease develop, or resistant plants may become infected but disease remains very minor and does not progress as rapidly as in susceptible cultivars.

Table 1. Ribes spp. with resistance to white pine blister rust

Red & white currant
Ribes sativum or Ribes rubrum
Black currant
Ribes nigrum
Gooseberry
Ribes uva-crispa or Ribes hirtellum
Black currant x gooseberry
R. x Nidigrolaria
Red Lake
Rondom
Viking
White imperial
Ben Lomond
Ben Sarek
Consort
Coronet
Crusador
Doch Siberyachki (Daughter of Siberia)
Kosmicheskaya
Lowes Auslese
Minaj Shmyrev
Pilot Aleksandr
Mamkin
Polar
Risager
Titania
Willoughby
Achilles
Captivator
Columbus
Colossal
Downing
Glenton Green
Golda
Hinnonmaen keltainen
Howard's Lancer
Jahn's Prairie
Jeanne
Josselyn
Oregon
Pixwell
Poorman
Sabine
Whitesmith
Jostaberry

Cultural control

Reduce moisture on white pine needles

Landscape planning

2016

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