Fungus attacks local aspens
September 25, 2015
It’s late September in Park City — time for Park Record photographer Jake Shane to start looking for shots of aspens in all their golden glory.
This isn’t one of them.
Around Park City this year, hikers and homeowners have reported an odd phenomenon: aspen leaves turning brown and dropping off long before fall officially arrived. The blight has affected both landscape trees and tracts of indigenous aspens in the mountains.
"In 30 years here, we’ve never seen this," one Deer Valley homeowner said in an email to The Park Record. "Our aspens have fewer leaves than usual and the leaves that are left have black spots and they are shrunken.
"When I look across the canyon, at the trees on the hills of Deer Valley and Park City Mountain, they seem to have the same look."
So what’s the deal?
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Well, there’s a fungus among us, according to PJ Abraham, area forester for Forestry, Fire & State Lands
"It is basically a foliar fungus that attacks the aspen," says Abraham. "It attacks the trees in the springtime when the trees are budding out. The fungus spreads on the leaves, and then the leaves turn brown or black, and then they’ll fall right off."
The fungus is called Marssonina, and it’s nothing new in these parts, say Utah tree experts. In 1981, a "severe aspen leaf blight extended over large areas of northeastern Utah, southeastern Idaho and western Wyoming," says a research paper by the U.S. Forest Service. That year, foresters studied 1,000 acres of aspens in the Tony Grove Lake area of Logan Canyon and found about a third of the area to be completely defoliated and another third moderately affected. "Periodic outbreaks have been observed by pathologists and others in the middle Rocky Mountains since the early 1900s," researchers add.
"Yeah, it’s natural to the area," Abraham agrees. "It’s just when the conditions are there, it can take off. We typically see it every year in the mountains, along with ink spot (caused by the Ciborinia whetzelii fungus). There are a couple of other different types of fungus, but this year the Marssonina really took off."
The conditions this year, he says, included a wet spring that came at the same time that the aspens were budding and the Marssonina fungus was spreading its spores.
"People will notice some aspen trees are affected more than others, and that just depended on when those trees were budding out, the susceptibility of the trees, and when the fungus was releasing its spores."
Abraham, who is responsible for a five-county area including Daggett, Duchesne and Uinta counties, says he has seen some of the worst damage closer to his Heber City office.
"It’s really hit Summit and Wasatch counties hard. There are a lot of people asking about it."
The fungus is most apparent at elevations between about 6,500 and 8,000 feet, he says.
"If you can get up higher, above 8,000 feet, you’ll see better fall colors on the aspens because that fungus didn’t attack those really high trees as much."
He also notes that, on some of the damaged trees, the new growth has been more resistant to the fungus. "You’ll notice, at the tops of the trees, healthier-looking green leaves."
For those ready to start their chainsaws, Abraham suggests that next year should bring releaf, unless we get another wet spring.
"It’s more an aesthetic concern. It won’t necessarily kill the trees unless it hits the trees multiple years, and then it could possibly cause some mortality."
It’s ironic that, in the middle of a drought cycle, too much moisture is getting the blame for the Marssonina outbreak. But Abraham says the prolonged drought may be making the trees more vulnerable to insects and disease.
"What really affects the aspen trees is our snowpack … So, if we have a winter where we don’t have a lot of snowpack, that can really put a lot of stress on the aspen trees, because they don’t have the water reserves to build off of If we see another winter like we did last year, definitely those trees located on the lower elevations, south-facing aspect, are trees that will definitely be stressed."
According to one study cited by the U.S. Forest Service, native aspens also vary in their resistance to the Marssonina fungus depending on their clone. (Because native aspens propagate by sending out root runners, they are often genetically identical to the trees next door. So clumps of wild aspens often react to the fungus in concert with their neighbors.)
Abraham says that not much can be done to attack the fungus in the mountains. However, for homeowners with infected aspens on their property, he does have some advice: rake up the dead leaves and get rid of them.
"That will reduce the fungus that winters on the leaves and then decrease the chances of that happening the following year," he said.
"And also, if they have a really dense pocket of aspen, increasing the spacing between those trees or pruning the lower branches, so that there is more air-flow movement going through those trees, will also decrease the chance of the trees being attacked by the fungus."
Utah State University Extension tree experts also says that sprinkler irrigation should be strictly avoided because the splashing water spreads the fungal spores. However, experts have mixed opinions on the use of fungicides against Marssonina.
Abraham will be at the 6th annual Recycle Utah Harvest Fest at the High Star Ranch in Kamas on Saturday, Oct. 3, where, he says, he will be happy to answer questions.
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