By: Anthony C. Arnoldi, Board Certified Master Arborist WI-0102B
Conifers continue to stay in the news. Spruce had been the most noticeably affected by drought stress and disease agents up to now, but recently both pines and spruces are showing browning needles that affect their beauty and health. The culprit is a group of fungi collectively known as needlecasts.
This browning can develop slowly, over several years, or very rapidly, as has been the case this spring. These fungi attack the needles as they are emerging. Their spores are in the air in spring and land on the soft needles. If the needles are moistened often enough from rains or heavy dews, the spores are able to germinate and then attack the vulnerable tissue. In years when the frequency of moistening events is greater, there is more and faster browning from needlecasts. Drier springs reduce the amount of browning from needlecasts.
This spring has provided several rain events. Many Pines and Spruce have rapidly browned as a result, and many more will show progressive browning over the course of 2008. Their weakened state from previous years of drought stress has lowered their resistance to fungal attack and spread, further speeding the browning. Individual trees vary in their ability to resist disease, (as we do as well); therefore, the amount of browning will vary from tree to tree of the same species. Site conditions that favor fungal development such as shade, crowding, reduced air movement, etc., will have an effect also.
Infected needles show spotting or banding of discoloration, but then begin to brown, usually at the tip at first, but eventually spreading along the needle. When the needle dies, it is shed (“cast” off the tree). In Austrian and other pines, the fungus is usually Dothistroma. In Spruces, the needlecast is usually Rhizosphaera.
Needlecasts are controlled through protective fungicide spray programs. Timing and materials can vary with the species of needlecast. In the case of evergreens, patience is needed for both control and the return of aesthetics. Spraying protects the new growth that comes on in spring. Since evergreens carry at least five years of needles, when these become infected, it takes at least three consecutive years of the spray program to collect three years of protected and retained needles to have beauty return.
Many evergreens are needlessly removed by saddened homeowners or ignorant tree cutters who don’t realize that they can be saved. Don’t let this happen to you! Call your Wachtel Certified Arborist for the accurate diagnosis. Also, share this newsletter with your neighbors who may be thinking of cutting down their evergreens. Especially where these are providing needed screening between yards or obstructing unwanted views, this could be tragic.
© Copyright 2008 – Wachtel Tree Science & Service, Inc.