A few of the conferences I have attended this year were about some of the disease problems we have been seeing in Spruce, Pine, and Fir trees. Many times I get called in to look at a tree and, unfortunately, it is usually a post-mortem diagnosis. Evergreens show signs slowly and generally die quickly. The best treatment period for fine needle evergreens – the period in which you can have the greatest effect – is when those new candles emerge.
There are early signs of disease which you can recognize. Austrian Pines can be affected by the fungus Dothistroma which causes needle discoloration. White Pines, Scotch Pines, and Red Pines can be affected by Diplodia tip blight. The tips of the branches will hang over and discolor. In Blue Spruce we are seeing Rhizosphaera Needle Cast which causes the needles of the tree to discolor and then fall off – generally from the center and lower branches first.
The treatment for all of these diseases is similar. I utilize both systemic and contact fungicides to stem the spread of the disease. I cluster 3 treatments during the spring when the new needles emerge.