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by Kevin Strauss
The tall, majestic white pine (Pinus strombus) defines the northwoods with its 100-foot-tall trunks and wide branches. While these trees are the undisputed monarchs of the boarder country, there is an assassin in the palace. White pine blister rust (Cronartium ribicola) has been taking advantage of pines weakened by years of drought to infect the branches and trunks of our only five-needle pine.
This parasitic fungus originated in central Asia, where it infected a distant relative of the white pine. But through trade routes, the fungus migrated into Europe by 1842. The fungus then hitched a ride on white pine seedlings grown in Europe and arrived in New York state by the 1890’s. From there it spread across the country, reaching Minnesota in 1914. “Blister rust has been around for a long time,” said USFS Forester Ralph Bonde. “It is a concern, but it is nothing that we can’t work with.”
According to Bonde, infection rates aren’t all that bad in the Ely area, but they get worse the closer you get to Lake Superior, where moist conditions lead to more fungal infections.
Foresters have been working to develop a blister rust resistant white pine for the past 60 years and they have been having some success. Of the newer, more resistant white pines being planted by state, federal and private foresters, a smaller percentage seem to be contracting the infection.
“We are losing some trees to white pine blister rust, but we are always going to loose some trees,” said Bonde. “We a planting a lot of white pine in the forest as well.”
Recent drought years have been stressing pines, making them more susceptible to infection and allowing the disease to progress more quickly in infected trees. Several area residents have been noticing even more infected pines in the area.
When the spores infect a white pine, the resulting fungus plugs up the xylem (zi’-lum) and phloem (flow’-um) tubes that carry water and food just inside the bark in the branches and trunk of the tree. The infection is a little like the tree version of arteriosclerosis where plaque builds up in human arteries and impedes the movement of blood. While a tree can survive the loss of a branch to the infection, if the fungus reaches the trunk of the tree, the tree will most likely die. White pine seedlings are the most susceptible to this fungus which attacks their needles, but older trees can get it as well.
But the news isn’t all bad. Bonde reports seeing higher levels of natural regeneration among white pines along the North Arm Trail and Echo Trail north of Ely.
If you see a white pine with one branch of dead needles (“flagging”) it is probably infected with blister rust. Bonde recommends pruning all infected branches before the fungus reaches the trunk. He also recommends pruning the lower 9 feet of taller pines. For seedlings, trim the grass around the tree and prune the bottom ring of branches, so they aren’t in contact with the wet grass “microclimates” that make it easy for blister rust to infect the tree.
The Ely Timberjay
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