Tree decline, especially on evergreens and spruces, has been a hot topic over the last several years and I expect it to continue into the future.
Evergreens do not adapt well to extreme weather situations, partly because they have proportionally small root systems which make them less resilient to stressful situations.
The symptoms on established conifers are similar to those that can be observed on a cut Christmas tree. Even after the tree is placed outside following the holiday season the foliage remains green, sometimes for more than 5 months, without a single functioning root.
Only when warm temperatures arrive in late spring will the foliage on this cut tree start to lose moisture and turn brown. Once this process begins, the discoloration will continue until the tree is completely brown and the foliage falls off the branches. Until a significant portion of the crown turns brown, though, the casual observer may not notice the subtle change in needle color.
The same thing happens in landscape conifers when the roots or trunk is damaged. The structure of the needles, and the waxes that coat the foliage, help to inhibit moisture loss and the foliage remains green. If the root damage occurs when temperatures are cool, then the foliage can appear healthy for several weeks or months after the roots have died. By the time the foliage begins to turn brown the roots may have been dead for weeks or months.
Conifers often respond all at once when they reach some “critical threshold” of stress. Frequently, this is exacerbated by disturbances in the root area, drought or other environmental, site or cultural problems. Injury to cambial tissue (tissue that transports food and water) on thin-barked trees may also have occurred this past spring when unseasonably high temperatures in March were followed in April by a sudden drop in temperature. Delayed symptom expression consisting of branch dieback and even tree death is likely a result, in part, of the tissue damage that occurred following this extreme temperature fluctuation.
One clue to determining if a browning evergreen will produce new growth is to check the buds at the tips of the branches. If they are green inside, then new growth may develop in the spring. If the buds on the ends of all branches are brown and dry, the tree will not recover.
For more information on evergreens, visit: www.ppdl.purdue.edu/PPDL/pubs/briefs/Conifer-Dieback.pdf .
Stacy Clupper is the agriculture & natural resources extension educator and the county extension director of the Purdue Extension-Grant County. Contact her at 765-651-2413 or firstname.lastname@example.org.