Local ash trees falling prey to insect invasion

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This article was published 11/07/2017 (3102 days ago), so information in it may no longer be current.

AN invasive insect that has destroyed scores of black and mancana ash trees in the Pembina Valley this spring has arrived in Winnipeg.

Damage from the cottony ash psyllid can be seen lining the boulevards in front of the Canadian Museum for Human Rights at The Forks.

“We just found it last week,” City of Winnipeg forester Martha Barwinsky said. “We don’t know what that means yet,” in terms of what action the city will take or whether trees will have to be destroyed.

In Morden, 97 black and mancana ash trees have already been destroyed, and remaining trees are being sprayed to try to prevent further losses. Winkler plans to take out more than 50 trees and is half-done spraying the city in defence against the insect.

When people hear of an ash tree infestation, they usually think of the emerald ash borer, which has been mowing down trees in Eastern Canada and has now moved as far west as Thunder Bay, Ont.

However, the villain in this case is an aphid-like insect, native to Central Europe. It had been previously reported in Edmonton, Saskatoon and North Dakota. The insect feeds only on black and mancana ash trees. It weaves a white cottony substance on the leaf and essentially causes leaves to shrivel and fall off.

For example, along Israel Asper Way at The Forks, the centre median is treed with green ash that are still healthy as they are not susceptible to the cottony ash psyllid. But trees alongside the roadway are mancana and black ash, whose leaves are shriveled and covered with the psyllid’s cotton.

In Carman, where the local council wants to get rid of the healthy ash trees in its downtown, its trees are also green ash and not susceptible to the psyllid.

The irony is ash was the main tree used to replace elm trees in Winnipeg and surrounding urban centres after Dutch elm disease started destroying boulevard elms decades ago.

“Everyone went crazy planting ash trees. They were relatively fast growing, they were resistant to road salt and they were native to Manitoba,” said private arborist Ken Fosty. “Now it’s come full circle,” insofar as the ash trees are dying, too.

“Five trees across the street from my home are all gone,” said Morden Mayor Ken Wiebe, following that city’s ash tree removal program.

Urban centres cannot allow dead or dying trees to stand because of the danger they pose falling onto property or people. Morden is replacing its ash with six varieties of trees to prevent widescale destruction from insects or disease in the future, Wiebe said.

In Winkler, Peter Froese, director of works and operations, is hoping black ash trees that still have top leaves and some remaining foliage will survive. “Then the leaves can still feed the roots,” he said.

Barwinsky said Winnipeg officials are trying to determine the extent of the infestation before taking its next step, such as tree removal or spraying. “I suspect we’re going to lose some trees, but to what degree, I don’t know.”

She said she holds out hope the infestation won’t be as bad as one that struck Edmonton a few years ago, resulting in significant tree loss. The insect seems to do its greatest damage in dry conditions, she said.

Winnipeg has about 101,000 ash trees in boulevards and parks, of which about 15,000 are black or mancana ash. There are another 11,300 susceptible trees on private property, Barwinsky said.

Winkler and Morden have begun spray campaigns using an insecticidal soap called Trounce, which plugs up the insect’s breathing apparatus, said Fosty. “The soap film suffocates the little bastards,” he said.

However, Barwinsky is uncertain about the effectiveness of the spray. She has been in consultation with counterparts in Saskatoon who are experimenting with pesticide injections into the trees. “We really don’t have any idea how it got here,” she said.

The cottony ash psyllid may have migrated here through nursery stock, she said, adding she doubts it moved on firewood, as the insect isn’t a wood-borer.

bill.redekop@freepress.mb.ca