Aspen Fungal Foliage Diseases - "Many fungi are capable of attacking aspen leaves, from juvenile growth to senescence. However, only a few may be of local significance; and even then, their damage is of consequence only when they cause moderate to severe defoliation. Small trees suffer the most damage, and may be killed by repeated infections. Clonal susceptibility to individual foliage diseases is common, but under certain conditions, whole stands can become infected. Because these fungi kill areas of leaves and often cause premature defoliation, their damage is usually confined to reduced tree growth of severely infected trees. Therefore, in most areas, these diseases are not important in aspen management" (Christensen et al. 1951).
"Black leaf spot - caused by Marssonina populi (Lib.)Magn., is the most common leaf disease of quaking aspen in the West. Small brownish spots appear on the infected leaves in late July and early August. The spots later enlarge and turn blackish, and are of various sizes and irregular in outline, with a yellowish to golden border. Infection is usually more severe on smaller trees and in the lower crowns of larger trees. Light infection is common in many western stands, and clonal susceptibility is noticeable. Epidemic conditions are intensified by abundant rainfall in the spring and summer (Harniss and Nelson 1984, Mielke 1957). Twig and branch mortality after two severe infection years has been reported (Harniss and Nelson 1984, Mielke 1957). These epidemic situations may kill trees. However, the effect of leaf spot on overall aspen mortality is assumed to be of little consequence, because successive epidemic years are unusual, and even then mortality appears to be light. In most years, the annual infection repeats only in the lower crown, and usually late in the growing season." - Thomas E. Hinds
As Rob says of aspen and lawns, “The best defense is a good offense”. Shallow rooted aspen grow far from creeks and moist meadows in the continental climate of Colorado. In our far west, they are a riparian species. Aspen love deep soils, rich in organic matter & nitrogen, ample moisture and plentiful vegetation or mulch covering the ground far wider than the trees are tall. Because they frequently have insect pests and foliage diseases (and because they want to spread across the globe), they are best used in the farthest corner of a landscape, along the sunny back property line for their excellent fast growth and dense screening.
The golden fungal rusts (Melampsora spp.?) that usually affect the Lemmon’s willow in late August nearly every year, began in ernest in late June this year and have also been unusually rampant on Scouler’s willow. Stressed plants from dry winters (very low soil moisture) combined with the “abundant rainfall” is ideal for fungal foliage infections. It is unlikely the plants will suffer. Like their close relative aspen, willows thrive on water, food & mulch.
The golden spores of Melampsora willow rusts. Unusually rampant this summer of "abundant rainfall". Lemmon's willows almost always have this fungus in late August but it started in June this year and it is on most of our native species. it is NOT a worry. FB
Posted on Sat, August 15, 2015
by Eric Larusson filed under