In the springtime the willows weep with joy.

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While, come April, Evanston’s lawns begin to shimmer green with the first blades of spring, its emerald canopy remains just a promise folded in the buds of bare trees.

Persistent cold weather is the bane of impatient children and gardeners, too. But for City workers whose saws are creating a buzz in certain parts of town, March and April are high season.

Early spring is prime time for trimming and inspecting the City’s urban forest, says Paul D’Agostino, superintendant of Parks, Forestry and Facilities Management. His crews are out in full force.

Several factors make this season ideal for tree trimming. Since any tree can be trimmed while dormant, there are no restrictions this time of year, says Mr. D’Agostino. Making cuts in oaks or elms in summer, he says, “makes them vulnerable to disease.”

The structure of a leafless tree is more obvious, he adds, and “it’s easier to tell what’s dead. You can see the buds when you’re in the tree, though you can’t from the ground.”

Trimming trees a whole block at a time is most efficient, says Mr. D’Agostino. As many as two crews – 12 or 13 men – may work together. Mainly, they “trim for clearance,” he says, cutting branches away from houses, buildings and sidewalks. In only a few species, such as the honey locust, do crews practice selective thinning of branches. Twigs and branches are fed to the City’s several chippers. The bases of big trees are split into firewood.

“Ideally,” says Mr. D’Agostino, Evanston trees get a trimming every six to eight years. The devastation wreaked by the emerald ash borer has diverted workers, though, making 11 or 12 years the norm. Tree work slated for completion in northwest Evanston last winter continues this month, for example, because the need to remove infected ash trees took precedence over trimming.

The ash borer has killed about half the City’s population of ashes; once numbering 4,100, some 1,900 have been removed or tagged for removal, Mr. D’Agostino says. The only treatment for the ash borer is preventive, he says, and the City has “no budget to pre-treat.” Unable to stay ahead of the insect, foresters are left to follow some fine-feathered friends who are are canny clinicians. “We look for ashes with woodpecker damage,” says Mr. D’Agostino. Extensive holes are a sign the tree is infected and “the birds are going after the [ash borer] larvae.”

A slower-moving pest, the Asian longhorn beetle, is considered eradicated in Illinois, says Mr. D’Agostino. The bug was caught when it was confined to certain areas, with trees removed outward from an infected branch. The tactic worked; no longhorn beetles have been spotted in several years.

Evanston’s elm-injection program has had amazing success as well. Trees injected regularly since 2005 have a 99 percent survival rate, says Mr. D’Agostino. As a result, City Council just funded an extension of the program to all public elm trees with trunks 10 inches in diameter or larger.

The City’s tree-planting budget was recently halved, from $160,000 to $80,000. But a grant application resulted in a $30,000 award from U.S. Senator Dick Durbin to replace ash trees. Crews will plant 300 trees this spring and about half that many next fall. “We’re still planting more than other cities, who have almost eliminated tree planting,” says Mr. D’Agostino.

In Evanston’s public places, grass is mostly left alone. Once or twice a year organic fertilizer is applied. But for some 15 years the City has refrained from putting any pesticide at all in its parks. The rare exceptions, Mr. D’Agostino says, are the Merrick Rose Garden, where herbicide is applied to keep the weeds down, and some sports fields, where herbicide becomes a last resort in eliminating weeds from playing surfaces where soil compaction makes grass hard to grow.

A new crop of dandelions will soon paint the parks yellow. Untamed by herbicides, they arise trim and golden, then fade to a scraggly gray. A sure sign of spring, they are also a reminder that the City subscribes to a safe Integrated Pest Management System meant to ensure that Evanston’s trees and grass will continue to flourish.