Suppression of Spruce Needle Blight in Coastal Alaska

Abstract

To evaluate the efficacy of disease suppression, three fungicides were applied to 72 young Sitka spruce trees near Juneau, Alaska in an area of endemic infection by the needle blight fungus, Lirula macrospora. Treatments were applied to three branches shortly after spruce needles emerged in spring and, on one-half of the trees, again during shoot elongation. Trees treated with each of the three fungicides had significantly fewer dead needles one year after infection than did trees treated with the control. Needle death did not differ significantly among the three fungicides or on trees that were sprayed once compared to trees sprayed twice. None of the three fungicides caused observable injury to spruce tissues, nor significantly altered the shoot growth of sprayed trees. These results suggest that the disease can be controlled by applying chemical treatment at the correct time in spring shortly after bud break of spruce.