Many trees are a feast for the eyes, lush and green from all the growing season’s rain. But some people are seeing spots on their tree leaves caused by this year’s wet weather – although it’s nothing to worry about, experts say.
On the other hand, “we’re seeing some other freakish things,” said community forester Tim McDonnell.
Some trees, including ornamental pears, are dying this summer from earlier causes than this year’s rain: either the sudden and dramatic temperature drop in November, when many trees were growing lushly, or the drought dating back a few years.
Some Osage oranges – a normally stalwart tree – have had whole sections dying, and it’s not known yet what the cause is, McDonnell said.
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“As we said after the drought, we’re going to see a lot of things happen for the next four or five years. We’re in the middle of it.”
Among the leaf funguses that are being seen are mycosphaerella leaf spot on ash and Boryosphaeria canker of oak, especially pin oak. The leaf spot shows up as orangey-brown spots on leaves, and the bot canker turns leaves on the ends of branches brown, said master gardener Sue Hansen. Nothing can be done for the conditions, which should not harm the trees.
The die-back of the bot canker – dead new growth on the end of a branch – “is the most obvious, because it’s in your face,” said extension agent Matthew McKernan. And the dead leaves are not going to fall off, he said. It’s mainly aesthetic damage that can be pruned off, or you can wait for new growth next year eventually to overtake the dead.
The leaf spot on ash and walnut is not typically seen on trees in this area and is due to the heavy spring rains, McKernan said.
In addition, “there’s a lot of rust that we don’t typically see that we’ve been seeing on ornamental pears,” McDonnell said, along with a little bit on ash. “A lot of trees look good, but there’s some spotting on trees. Nothing can be done about it. Leaf diseases you don’t get too worked up about unless you have them year after year after year.”
Some of the ornamental pears are suffering a much worse fate.
“We’ve seen a lot of bark damage to ornamental pears,” McKernan said, probably caused by the cold snap in November. And the bark damage is killing most of the trees. (Some of them also have extra bark damage from human error that can afflict any tree – such as the injury of a weed-whacker whipping against the trunk.)
Conifers also looked worse and worse going into spring, but some are looking better now, McDonnell said. He’s also seeing renewed signs of pine wilt on remaining Scotch pines after a bit of a respite.
Among other various problems with trees: sun-scorch toward the tips from several weeks ago, when we had hot dry weather; elm flea weevils that shouldn’t do enough damage to worry about; and iron chlorosis. The chlorosis, which causes yellow leaves, is a common problem in any year but is also made worse by excessive moisture, McKernan said. Injection gives the fastest results, but the pH of the soil also can be adjusted with sulphur to correct the problem, he said.
McDonnell said people should not worry about doing too much for trees at this point. The trees should have had adequate moisture – sometimes too much. “I’m hoping people have cut back on turf irrigation, because the trees have probably gotten enough.
“Don’t let the trees come under stress. ... Don’t push them anymore” with water or fertilizer, unless there’s a known nutrient deficiency, he said. “If it’s stressed, I wouldn’t push it anymore.”