First came the bark beetle, which began decimating the Twin Cities’ canopy of elm trees decades ago.
Then came the emerald ash borer, which continues to take its toll. In Minneapolis alone, 760 ash trees will be taken down this winter, including 200 trees at the Fort Snelling Golf Course operated by the Minneapolis Park and Recreation Board.
And next up?
Get ready for the Asian long-horned beetle, an inch-and-a-half-long bug that loves just about any kind of tree but is especially fond of maples. It will, however, make do with elms, ash, birches, poplars and most other hardwoods.
Because the beetle lives deep inside of the tree, the only way to stop it is to remove all of the trees in the infected area, says Ralph Sievert, director of forestry for the park and recreation board. His department is in charge of all the trees along the boulevards and in the parks.
The Asian long-horned beetle already has been a problem in New York and New Jersey and is moving west. It’s now in Ohio and has shown up the in Chicago area.
The beetle has not yet been detected in our area but Chicago is not that far away as the bug flies. And this bug does fly.
Ash threat to continue
In addition to the infected ash trees, crews will also be removing “challenged” ash with scarred trunks, die-back and those trimmed to make room for overhead wires. Such trees are frequently the first stop for the ash borer.
“Ash trees were a great replacement for the Elms,” said Sievert. “They were big trees and they grew fast.”
But, like the elm, the ash also had an insect in its future.
“The doom-and-gloom scenario is that the emerald ash borer population will continue to grow,” he said, adding that increased woodpecker activity can be the first noticeable sign of the borer but by then, it’s usually too late.
“By the time you detect it in the tree, it’s been there for three years,” Sievert said. It is not unusual for the borer to go undetected in wooded areas, like those along the river, and then move to the ash trees on the boulevards and in parks and yards.
It has not been a bad year for the elms, in part because there aren’t that many left to become infected. This year, 907 elms will be removed from boulevards and parks, about half or a third of the usual number infected.
Tree variety the key
All of these tree threats have taught us a lesson. We need to plant a variety of trees in our neighborhoods and park to hedge our bets. And that is exactly what the park board has done this summer in North Minneapolis.
To replace the trees destroyed by the 2011 tornado, the board planted 3,200 trees, and rather than lining a street with a single variety, staffers have mixed up the bouquet.
Each block received two or three types, including flowering crab, honey locusts, river birch, bi-color oak and a tree developed in North Dakota called the Prairie Horizon Manchurian alder.
All of those trees have been watered every 10 days this past summer by the park board and have been fitted with a watering bag, which will hold 20 gallons. The bag allows water to seep slowly into the ground at the base of a tree.
“You can see how much better the trees look,” said Sievert, who notes that even so, the city won’t know until spring how many trees the dry weather has claimed.
Trees still need watering
As a result of the dry summer and fall, the city’s trees still need water.
“We always tell folks to water the trees every week until the ground freezes,” said Sievert.
“The most important roots are in the top 18 to 20 inches of the ground,” said Sievert, “a hose trickling near the base of the tree is good.”
The park board estimates that it costs about $3 to water one tree weekly throughout the growing season.
“We were planting trees in early October, and the soil was like powder it was so dry,” said Sievert, who has seen signs of distress in once-healthy trees. Leaves look scorched and cupped. The crown of the tree starts to thin and the leaves drop earlier than usual. All of this makes trees more susceptible to disease.