If trees could talk, the red pines in the St. Croix River Valley would tell a tale of woe.
Two successive summers of drought combined with the area’s sandy soil have left them too parched to retain as much moisture as they normally would over the long, cold winters that have followed.
As a result, large stands of pines appear to be dying in Washington County. The damage extends from Taylors Falls — north of Stillwater — south along the Mississippi to southeastern Minnesota. Their green needles have turned red and are falling off. And those trees that failed to produce new growth this past spring most likely have died, according to two area tree disease experts, meaning all of this year’s snow and heavy rain may have come too late.
The situation could worsen dramatically for two reasons. Stressed trees act like beacons to pine bark beetles and to a tree root fungus lurking in Wisconsin forests. Either one could kill off those trees that survived extreme weather conditions.
“Once a tree is infested [with pine bark beetles], there is very little that can be done effectively to save it,” said Chris Muehleck, district manager of St. Croix SavATree, which has offices in Roberts, Wis., and Hopkins.
Annosum root rot, caused by the fungus, Heterobasidion irregulare, has been found in conifers in Wisconsin since 1993, according to the Wisconsin Department of Natural Resources. The disease causes the most damage in plantation-grown conifers (especially pines). Tree stumps offer a place for infection to start. Connected roots provide a pathway for annosum root rot to move underground from tree to tree, according to the Wisconsin DNR website.
Where roots connect, the disease moves from tree to tree at the rate of 3.2 to 6.5 feet per year, the website says. Infected trees are shorter and more slender than healthy ones, have fewer leaves and less shoot growth.
“It’s underground and very, very difficult to control. This is why we need to act quickly,” University of Minnesota plant pathology professor Robert Blanchette said of the fungus. “Once it’s established, it’s very hard to eliminate.”
The disease has also been attacking trees on the East and West coasts, Blanchette said.
It takes several years for evidence of the fungus — fruiting bodies that release spores into the air — to show up on dead and dying trees, according to Blanchette. He expects some of those spores may have already crossed the St. Croix.
Temperatures between 41 and 90 degrees encourage spore production, according to the Wisconsin DNR. The wind can carry the spores over hundreds of miles, although most only move to within 300 feet of their host tree.
Blanchette and his fellow researchers at the university are searching for the disease among Minnesota’s red and white pines. He has applied for a $371,840 grant from the Minnesota Environment and Natural Resources Trust Fund to research early detection of the fungus and prevent its spread. The work would run for three years beginning in July 2015.
Despite its eradication and treatment programs, the Wisconsin DNR has not been able to keep up with the disease, according to Blanchette.
Annosum root rot has killed pines and spruces in 24 Wisconsin counties, including Buffalo, Trempealeau and La Crosse counties, which are directly across the Mississippi from Goodhue, Wabasha and Winona counties in southeastern Minnesota.
The disease causes more than $1 billion in losses annually in the United States, and has tremendous ecological effects on forest health and productivity, the grant application states.
Blanchette hopes to develop a molecular detection method to quickly and reliably identify the fungus in wood samples. The grant would also fund surveys of the areas around affected trees and the establishment of guidelines to manage the disease.
Blanchette also plans to fight fungi with fungi, using native fungal species to compete against the invading Heterobasidion.
For disease control to succeed, Blanchette said his team would need the assistance of foresters, arborists, master gardeners and the public. Part of the grant would fund training, developing sampling protocol and setting up the U’s Plant Disease Clinic on the St. Paul campus to run tests.
Blanchette and Muehleck said the public could protect trees on their properties from beetles and fungus by adding two to four inches of wood mulch around the base of each tree and by watering regularly. The finer roots of a tree, which grow within the top 12 inches of soil, absorb the most water and nutrition, according to Muehleck.
“Irrigation is the best thing,” he said. “In naturally occurring large stands, this is impractical.”
Nancy Crotti is a Twin Cities freelance writer