Some trees suffering from non-lethal leaf blight

Austin Colbert
Some aspen and cottonwood tree leaves, like these found near Steamboat Springs High School, are suffering from a fungal disease that could impact their colors this fall. The infection, which is not lethal to the trees, developed because of the extra damp and cool weather this year.
Austin Colbert

— Illness is never becoming of a person, and the same holds true for plants. While most of the aspen and cottonwood trees near Steamboat Springs look to be on track for their annual fall photo shoots, the yellows and golds growing more abundant each night, there are a few suffering from an un-charming form of leaf blight.

State biologists have seen above average cases of at least two fungal diseases in the trees this fall, which can cause the leaves to develop dark spots or flecks.

“The good news is that these diseases rarely cause any permanent tree damage or death,” said Dan West, an entomologist with the Colorado State Forest Service, in a news release. “But this is the highest level our foresters have seen in many years for some parts of the state.”

The two diseases recognized are Marssonina, the most common disease found in Colorado aspens and cottonwoods, and Septoria, most commonly found in cottonwoods. Both diseases cause similar looking spots on the leaves, which are usually brown or black in color.

The diseases are not lethal to the trees, and will only impact the way the leaves look this fall, on top of occasional premature de-leafing.

“This is a natural phenomenon, and despite how they look, these trees should leaf out again next year,” West said.

The reason for the unusually high volume of these diseases is due to the area’s unusually wet spring and early summer. The fungi flourish in the cool, damp conditions, but should leave no lasting impact on the forest.

There are ways to prevent future cases of the leaf blight, such as raking up fallen leaves and the use of fungicide, none of which will help lessen the spread this fall.

The leaves will continue to change colors over the coming month before falling off as colder weather sets in. While some of the highest peaks in the area have seem some snowfall, the Yampa Valley isn’t likely to see any significant winter weather until mid-October, at the earliest.

Last year’s first major snowfall came Nov. 24, with nine inches. In 2013, the first snowfall occurred Oct. 4 with 14 inches.

To reach Austin Colbert, call 970-871-4204, email or follow him on Twitter @Austin_Colbert

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