Spruces of various species are popular landscape trees in southwest Missouri, according to Patrick Byers, a horticulture specialist with University of Missouri Extension. Byers believes that Norway spruces that are adapted to southwest Missouri and Colorado blue spruce, which are not as well adapted but are a lovely tree, are the most popular in this region.
Unfortunately, several common diseases have impacted spruces in southwest Missouri with conditions during the last several years very favorable for these diseases. "Spruce needle cast is something that the blue spruce is very susceptible to but the Norway spruce is resistant to," said Byers.
Symptoms of spruce needle cast include the loss of needles. Close examination of the infected needles will reveal tiny black dots (the fruiting bodies of the fungus). A key symptom is the sudden appearance of needle drop. "Trees are rarely killed by Rhizosphaera needle cast, but several years of attack will take its toll and only the current season needles may remain," said Byers.
Copper-based fungicides, such as Bordeaux or Mancozeb, are currently registered and effective as a preventive control against this disease. Byers recommends beginning applications when new needles are half grown and again when needles are fully expanded, about three weeks later.
Cytospora canker is another common disease which causes entire branches to die. Lots of whitish pitch will appear on the trunk, where cankers are located.
"You can reduce stress on the trees, but little can be done to save the infected branches and the tree may be lost," said Byers.
For more information on this topic, or to ask other lawn or gardening questions, contact the Master Gardeners of Greene County hotline at (417) 881-8909.