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White pine blister rust

Quick facts

  • White pine blister rust (WPBR) kills branches, tree tops and whole trees of Eastern white pine and causes leaf spots and leaf loss in currant and gooseberry plants.
  • WPBR can be found throughout Minnesota but is most common in northern and eastern Minnesota where cool moist conditions in late summer favor infection.
  • WPBR needs to infect both a currant or gooseberry plant and a white pine to complete its life cycle.
  • Diseased pine branches should be pruned out of the tree before the infection comes within 4 inches of the main trunk.
  • Disease resistant currant and gooseberry bushes are available.

How to identify white pine blister rust

Symptoms on Eastern white pine (Pinus strobus)

  • All needles on one or more individual branches first turn yellow, then rusty red.

  • The branch with the dead needles will have a canker which is a swollen area with discolored and cracked bark.

  • Cankers on the main trunk are oval or diamond-shaped and often have a dead branch in the center.

  • Sticky, clear-to-white sap oozes from the canker and drips from the infected branch or runs down the trunk.

  • In spring, white-to-yellow blisters form at the edge of the canker and release powdery orange spores.

  • Gummy, orange droplets containing spores may be seen along the canker in summer.

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

  • Angular, yellow leaf spots that are contained by leaf veins can be seen on the upper leaf surface.

  • Raised, orange pustules can be seen on the underside of the leaf spot.

  • By late summer or early fall, orange or brown, hair-like tendrils form amongst the orange pustules on the underside of the leaf.

  • Severely infected leaves or leaves on highly susceptible varieties may fall off during the growing season.

Plants affected by white pine blister rust in Minnesota

  • Eastern white pine (Pinus strobus) and other five-needle pines.

  • Currants and gooseberries (Ribes spp.), indian paintbrush (Castilleja spp.) and lousewort (Pedicularis spp.).

How does White pine blister rust survive and spread?

The white pine blister rust fungus Cronartium ribicola needs to infect both white pine and a Ribes spp. plant to complete its life cycle.

White pine infection

  1. Spores from infected Ribes spp. plants are carried to white pine trees on cool, moist air currents in late summer or fall.

  2. These spores infect pine needles if moisture is present.

  3. The fungus eventually kills the needle and moves into the shoot or branch where a canker is formed.

  4. The canker will girdle the branch, resulting in death of all needles on that branch.

  5. The infection progresses through the branch towards the main trunk travelling about 3 inches a year.

  6. The infection will continue into the main trunk.
    1. Seedlings and small trees are in great danger of dying from this disease when a canker girdles the main stem.

    2. Girdling stem cankers on older trees result in top-killing and the death of branches but this is usually not life-threatening.

  7. In the first summer after infection of the pine tree, gummy, orange droplets full of fungal spores may be seen on branch cankers.

  8. The second spring after infection, white, blister-like structures form at the edge of the canker. These fungal structures (aecia) crack open to release powdery yellow orange spores called aeciospores.

  9. These spores can be carried long distances on wind currents to infect Ribes spp.

Ribes spp. infection

  1. The powdery yellow orange aeciospores produced on infected pine trees are carried by wind to infect the leaves of Ribes spp. The infection causes yellow leaf spots and sometimes leaf loss.

  2. Just two weeks after infection, the white pine blister rust fungus creates a new type of spore, called a urediniospore, on the underside of infected Ribes leaves.

    1. Urediniospores can only infect Ribes leaves. The production of these spores results in new leaf spots within the plant canopy and in neighboring plants.

  3. When the days begin to shorten and temperatures drop, the white pine blister rust fungus produces short hair-like structures on the underside of infected Ribes leaves, called telia.

  4. Telia produce yet another type of spore, known as a basidiospore.

  5. Basidiospores are somewhat fragile and need cool moist air currents to carry them to nearby white pines.

How to manage white pine blister rust

Prune off diseased branches

  • Examine white pines each year for blister rust flags and cankers.

  • Prune off branches with cankers at a branch union or where the branch meets the trunk. Remove at least 4 inches of healthy wood beyond the visible symptoms of disease.

  • Infected branches don’t require any special kind of disposal because the pathogen cannot survive in dead wood.

Reduce moisture on white pine needles

  • Remove lower branches gradually as the trees mature. Young trees will need to be pruned slowly over the years. Make sure to never remove more than 1/3 of the canopy at a time. At least 9 feet of trunk should be visible between the ground and lowest branches of mature trees.

  • When planting white pine trees, space plants to promote good air movement around the trees.

  • Redirect lawn sprinklers or irrigation systems to avoid wetting pine needles.

Landscape planning

  • Don’t plant eastern white pine and currants or gooseberry together in the landscape unless resistant cultivars are used.

  • Avoid planting white pine in low lying areas or cold pockets.

  • Plant new white pine trees underneath the canopy of older trees, but allow enough light for growth of the planted trees. The combination of shade and some sunlight will shelter the planted pine from the evening dew and help to promote growth of the newly planted trees.

Plant resistant varieties

'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 are available that are resistant to white pine blister rust. Some of these plants have complete resistance and develop no symptoms of disease. Other resistant plants become infected but the disease remains very minor and doesn’t progress as fast as in susceptible varieties.

Ribes spp. with resistance to white pine blister rust

Red and white currant (Ribes sativum or Ribes rubrum)

  • Red Lake

  • Rondom

  • Viking

  • White imperial

Black currant (Ribes nigrum)

  • Ben Lomond

  • Ben Sarek

  • Consort

  • Coronet

  • Crusador

  • Doch Siberyachki (Daughter of Siberia)

  • Kosmicheskaya

  • Lowes Auslese

  • Minaj Shmyrev

  • Pilot Aleksandr

  • Mamkin

  • Polar

  • Risager

  • Titania

  • Willoughby

Gooseberry (Ribes uva-crispa or Ribes hirtellum)

  • Achilles

  • Captivator

  • Columbus

  • Colossal

  • Downing

  • Glenton Green

  • Golda

  • Hinnonmaen keltainen

  • Howard's Lancer

  • Jahn's Prairie

  • Jeanne

  • Josselyn

  • Oregon

  • Pixwell

  • Poorman

  • Sabine

  • Whitesmith

Black currant x gooseberry (Ribes x nidigrolaria)

  • Jostaberry

Rebecca Koetter and Michelle Grabowski, Extension educator

Reviewed in 2019

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