Newspaper article Pittsburgh Post-Gazette (Pittsburgh, PA)

Rain, Heat Hurting Planetrees

Newspaper article Pittsburgh Post-Gazette (Pittsburgh, PA)

Rain, Heat Hurting Planetrees

Article excerpt

Q. A number of young London planetrees have been planted as street trees in my neighborhood, and I am very concerned about them. They have a lot of yellow leaves, and many leaves have turned completely brown and fallen off. It almost looks like fall with all of the leaves lying the street and sidewalks. Is there some kind of blight affecting them?

A. If you look at the London planetrees (Platanus x acerifolia) that are planted as street trees around the city, you will notice that all of them look like the ones on your street. Young trees as well as old, established ones are suffering from a combination of issues.

Sycamore anthracnose is a very common disease on our native sycamores (Platanus occidentalis), which are closely related to London planetrees. Since planetrees are much more resistant to this disease, they are planted more often than sycamores. But resistant does not mean immune, and extremely wet weather in June and early July created very favorable conditions for anthracnose. Fortunately, it was hot and relatively dry in May when these trees were leafing out; otherwise, anthracnose would have been more severe because new leaves are much more susceptible.

London planetrees are also susceptible to powdery mildew, and we have had favorable conditions for that disease to develop. Fortunately, planetrees can live with both of these diseases, and only very high-value trees in situations that cannot tolerate any blemish require treatment.

The biggest issue, however, is drought and heat stress. The symptoms you describe appeared very suddenly, when the weather turned hot and dry in the second half of July. The overabundant rains of June and early July created a situation that kept soil saturated, which probably caused some of the trees' fine feeder roots to rot and die. Fine feeder roots are responsible for absorbing water and nutrients from the soil, and represent the largest mass of a tree's root system.

The plentiful rain also pushed more new growth than normal, and such succulent growth uses more water than hardened-off, mature foliage does. When the weather suddenly turned hot and dry, the trees had no time to adapt. …

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