Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
6/5/00
Contacts:
Paula Flynn, Extension Plant Pathology, (515) 294-0581,
pflynn@iastate.edu
Elaine Edwards, Extension Communications Systems, (515)
294-5168, eedwards@iastate.edu
Yard and Garden Column for the Week Beginning June 9, 2000
Tree Leaves with Problems
By Paula Flynn
Extension Plant Pathologist
Iowa State University Extension
This spring, many Iowans have noticed some emerging tree leaves are not conforming to their usual shape and color. Others have observed healthy leaves falling from trees in the middle of May. Do we need to revise the manuals of woody landscape plants to include accounts of such variation?
For those with a good memory, these events are very reminiscent of the spring of 1998. By now we should be able to explain these occurrences with certainty, right? Well, not exactly. Although the symptoms may resemble those caused by insects and diseases, insects and disease agents have not been found in most cases.
Blackened Leaves
A range of symptoms has been observed. Deciduous tree species such as maple, oak, walnut and ash have shown areas of black or brown leaf tissue, often at the edges or margins of the leaves. In other cases, entire leaves appear black or show a few spots.
The widespread occurrence of these leaf symptoms suggests a weather-related incident, possibly low temperature injury to newly developing tissue. Recall that much of the state experienced a few low temperature events intermingled with unusually warm spring weather. Low temperatures can cause tender, newly emerging leaves to turn brown or black, shrivel and eventually fall from the tree. The stem tissue connected to the leaves also may drop. The good news is deciduous trees can put out new leaves from other buds, camouflaging early season damage.
Deformed Leaves
Some trees, primarily oak and hackberry, have been putting out leaves that appear to be missing something -- most of the green leaf tissue. The major veins are present, but are surrounded only by a thin strip of leaf tissue. Because the overall canopy of the tree tends to show a thin, lacy appearance, this condition is commonly referred to as tatters.
These strange leaves appear as the new growth begins to emerge in May. Again, flushes of leaves that emerge later usually appear to be normal. These symptoms have shown up in rural forested areas and on individual trees in home landscapes.
The specific cause of tatters is not known. It appears the damage occurs when the leaf tissue is still in the bud or as it begins to emerge. Some potential causes include injury by cold temperatures, insects or herbicides.
Neighboring trees might differ in the problem development because they may be at slightly different stages of growth when the damaging factor occurs.
Other Damage
Blaming all spots and deformities on the weather would be somewhat unfair to the fungi, insects and drifting herbicides that also have made themselves known on occasion this spring. Moisture-loving fungi that cause leaf spots, blights and anthracnose have remained fairly quiet this spring because of the early dry conditions. Insects that feed on foliage often leave behind clues of their presence in the form of webbing, frass or the insects themselves may be present. When trying to decide if deformed, leathery leaves are the result of wayward herbicides, check other nearby plant species for similar symptoms.
What to Do
Fortunately, panic alarms can be turned off. Most established trees can withstand these setbacks, and using big doses of fertilizers or pesticides are not helpful or recommended. Waiting and watching will usually lead to trees that look normal by midsummer. Proper mulching and watering when extended dry conditions occur can help the overall vigor of trees.
ml: isugarden
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