Tree Diseases Will Affect Fall Colors Photos

ASPEN TREESSome stands of aspen and cottonwood trees across northern Colorado and along the Front Range won’t be their most picturesque this fall, due to leaf spot diseases that benefited from an unusually wet spring and early summer. For about the past month, foresters have been seeing an unusually high degree of leaf blight in the mountains and along the Front Range, as far south as Aspen, the Collegiate Peaks and Colorado Springs. At least two fungal diseases are to blame. Marssonina leaf spot is caused by the Marssonina fungus and is the most common leaf disease of aspen and cottonwoods in Colorado. The disease can be identified by the presence of dark brown spots or flecks on leaves, which can then fuse into large, black splotches on severely infected leaves. Also active now, mainly on Colorado’s cottonwoods, the Septoria fungus initially causes tan spots that become irregular brown-to-black spots coalescing to cover much of the leaf by late summer. While the diseases rarely cause permanent damage to the trees, foresters say this year’s trees will be less desirable as photo targets.

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