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Nightmare for elm trees

Posted on June 8, 2016 by Dave Mabell
Lethbridge Herald photo by Ian Martens A pedestrian walks by a row of elm trees suffering with relatively leafless and dark branches along a southside street. A local horticulturalist is sounding the warning about European elm scale that is attacking a number of trees among the city’s extensive urban elm forest.

For generations, stately elm trees have graced Lethbridge locations like Gyro Park and North Parkside Drive. City officials estimate there are 11,000 elms in the city, about half of them on residents’ property.
But now many of them are endangered by an insect that’s attacking the trees, covering their leaves and bark in a black mold. It’s called the European elm scale, and city arbourists believe the mild winter has allowed more of the bugs to survive — increasing the danger.
Southern Alberta horticulturalist Lyndon Penner warns the city as well as affected homeowners must act promptly to control the damage.
If not, he says, the trees “will not only continue to decline, but many of them may die.”
“I shudder to think what our streets would look like without our elms.”
Penner, a CBC radio horticultural expert and author, met concerned residents of Lethbridge on Monday. While planting a new elm will benefit future generations, he pointed out, it could be 60 years before it grows to the size of the Lethbridge elms now afflicted by the insect.
Acknowledging the situation, the city plans to inject the pesticide TreeAzin in about 600 trees in parks, boulevards or on other city land. Residents concerned about an elm on city property near their home may email that information to trees@lethbridge.ca.
For elms under attack on their own property, officials add, residents should call a qualified arbourist to provide a pesticide injection. They describe the adult insects as about 10 millimetres long, oval-shaped and a grey-brown colour with a “white waxy fringe.”
The “honeydew” they expel may cover sidewalks, patios and vehicles as well as the endangered tree.
To help trees overcome the insect’s attack, officials say it’s vital that owners water their trees regularly, especially during dry periods. It’s also important to avoid damaging their roots during landscaping or planting, they add. Providing mulch around the base also helps.
The city is assessing elm trees on its property to identify threatened trees. Evaluation and treatment will continue over the summer.

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