NEEDLE CAST DISEASE OF COLORADO BLUE SPRUCE

COLORADO BLUE SPRUCE IN THE FROT YARD...

NEEDLE CAST STARTS WITH A BLUE-GRAY DISCOLORATION OF NEEDLES... 

...THAT PROGRESSES TO YELLOW AND BROWN NEEDLES...

...AND DEATH OF ENTIRE LOWER BRANCHES

Monday, 8:15 AM.  31 degrees F at the ferry dock, 25 on the back porch.  Wind ENE, gusty.  The sky is overcast, the humidity rising, now at 79%.  The barometer is still headed downward, now at 29.91".  The storm in the northern Pacific is indeed sending cold temperatures and snow our way, and there is a storm warning for ten to twenty inches of snow driven by high winds for our region, from this afternoon through Wednesday.  We have to go to Duluth today, and Spooner tomorrow.  We'll make Duluth O.K. but will have to opt out of Spooner.
   When we moved into our new home fifteen years ago I planted a small, potted Colorado blue spruce (Picea pungens) that I bought somewhere between Dayton, Ohio and Bayfield.  A patented variety that I don't recall the name of, it has grown like Topsy into a slender, steel blue spire,  and become a focal point in the landscape.  Recently I noticed to my dismay that some of its lower branches were losing their needles.  Upon close examination I determined that the tree is infected with needle cast, a serious fungal disease of Colorado blue spruce.
   The disease is technically named Rhizosphaera kalkhoffii.  It has become a serious problem in the more southern regions of the state, but I had not seen it this far north.  The disease is spread primarily in  wet weather by fungal spores, and once a tree is infected the spores are spread about the tree by the splashing of raindrops.  The disease will disfigure the tree branch by branch, usually progressing from the bottom of the tree upward, and if not controlled will eventually kill the tree.
  The disease can be contained by increasing the air circulation around the tree, and by removing affected branches and either disposing of them in the garbage or burning them, and also spraying thoroughly with Bordeaux mixture (coper sulphate, lime and water) in the spring.  As always, pruning tools should be sterilized with alcohol or bleach after each cut.
   Colorado blue spruce, native to the western mountains, are over-planted as an ornamental tree, but are very valuable once established in the landscape.  White spruce, Picea glauca, native to the upper Midwest, eastern Canada and the eastern mountains, is less susceptible to needle cast and is a good substitute for Colorado spruce.
   For more information, go to the New Mexico State University Extension Guide H-163, available on the web.