You may have noticed that many the spruce trees in our area of southern New England have been dying lately. The cause is a fungal disease called Rhizosphaera needle cast. Like most needle cast diseases, Rhizosphaera infects the newly emerging needles of its host trees from older needles infected the previous year. The newly infected needles will grow normally through the current growing season and will not show signs of infection until the fungus matures to its spore producing stage, usually late winter or early spring of the following year, but sometimes as early as late fall of the current growing season. As you can see in the photograph below, the disease typically affects the lower portions of the tree first and progresses farther up the tree in subsequent years until the tree dies.
Not all spruce trees are equally susceptible to infection by Rhizosphaera. Colorado spruce (Picea pungens) is most susceptible. White spruce (Picea glauca) is somewhat susceptible and Norway spruce (Picea abies) very resistant to infection. Trees stressed by drought, poor cultural practices are more susceptible than healthy, vigorous trees.
Trees infected with Rhizosphaera can be effectively treated with well timed, preventive fungicide applications if the disease is caught early enough. Spruce trees typically retain three to five years worth of older needles that they need to photosynthesize enough food to maintain growth. Rhizosphaera kills the trees by causing these older needles to fall prematurely, slowly starving the tree. It may take several years of treatment to regenerate a full compliment of needles until the tree looks full and healthy again.
To learn more about Rhizosphaera needle cast, contact us or visit these websites: