Last week, Richard Jauron wrote about unusually high mortality of sour cherry trees this spring. Our calls and personal observations indicate that tree death is very common and widespread this year, and not just in cherries. In most cases, these trees were not actually flooded above ground level during last year's wet spell. Many species are affected, including ash, maple, hackberry, white pine, Douglas fir, Scots pine, black cherry, and others. Some of these trees failed to leaf out at all and their twigs are dry and crispy. Others have not leafed out, but the twigs are still pliable and green inside. Still others leafed out slowly or produced undersized leaves, then these leaves dried up. The crispy/dry cases are obvious no-hopers, but those that stilll have green, pliable twigs could still break bud and produce leaves.
What happened? Constant rain in 1993 left the ground waterlogged for long periods, which meant that little oxygen could reach tree roots. This lack of oxygen was especially acute in "heavy" soils with a high clay content. The striking aspect of this spring's tree mortality is that little of it was apparent last fall. A reasonable guess is that tress that had been weakened by waterlogging stress were ill-prepared to harden off normally during fall 1993, and that our very cold winter weather severely damaged or killed these stragglers.
What should you do for a tree that has defoliated, or struggled to put on foliage, but isn't dead? The best strategy is to wait and watch. If the weather stays dry, water deeply once per week, but more elaborate therapies are likely to be wasted and may actually increase stress on the ailing trees.
This article originally appeared in the May 25, 1994 issue, p. 80.