Over the last three weeks or so, Iowans throughout the state have been wondering what's wrong with their trees. Leaf samples sent to the Plant Disease Clinic showed a wide variety of brown spotting, marginal browning, and water soaking. Many species have been affected, including maple (most common), oak, hackberry, and ash. Leaf damage often occurs throughout the tree.
Some of the damage superficially resembles fungal leaf spots, but the cause is physical rather than fungal. Cold temperatures during one or more nights in early May, just as the leaves were emerging from the buds, damaged the tender young leaf tissue. Often, the injury took place before the leaves had unfolded fully, which explains why only certain parts of each leaf are damaged. Killed areas of the leaves ceased growing while undamaged areas continued to expand, gradually pushing some leaves into puckered and distorted shapes.
The encouraging news is that the cold injury is likely to have little effect on tree health. Some of the affected leaves may hang on all season, but the most severely damaged may fall and be replaced by new leaves. Despite the distressing appearance, this episode will be merely a tiny blip in a tree's life.
This article originally appeared in the June 9, 1995 issue, p. 85.