updated 7/14/2011 8:34:03 PM ET 2011-07-15T00:34:03

A recently approved herbicide called Imprelis, widely used by landscapers because it was thought to be environmentally friendly, has emerged as the leading suspect in the deaths of thousands of Norway spruce, eastern white pine and other trees on lawns and golf courses across the country.

Manufactured by DuPont and approved for sale last October by the federal Environmental Protection Agency, Imprelis is used for killing broadleaf weeds like dandelion and clover and is sold to lawn care professionals only. Reports of dying trees started surfacing around Memorial Day, prompting an inquiry by DuPont scientists.

“We are investigating the reports of these unfavorable tree symptoms,” said Kate Childress, a spokeswoman for DuPont. “Until this investigation is complete, it’s difficult to say what variables contributed to the symptoms.”

DuPont continues to sell the product, which is registered for use in all states except California and New York. The company said that there were many places where the product had been used without causing tree damage.

The E.P.A. has begun gathering information on the deaths from state officials and DuPont as well as through its own investigators. “E.P.A. is taking this very seriously,” the agency said in a statement.

In a June 17 letter to its landscape customers, Michael McDermott, a DuPont products official, seemed to put the onus for the tree deaths on workers applying Imprelis. He wrote that customers with affected trees might not have mixed the herbicide properly or might have combined it with other herbicides. DuPont officials have also suggested that the trees might come back, and have asked landscapers to leave them in the ground.

Mr. McDermott instructed customers in the letter not to apply the herbicide near Norway spruce or white pine, or places where the product might drift toward such trees or run off toward their roots.

'It's been devastating'
For some landscapers, the die-off has been catastrophic.

“It’s been devastating,” said Matt Coats, service manager for Underwood Nursery in Adrian, Mich. “We’ve made 1,000 applications and had 350 complaints of dead trees, and it’s climbing. I’ve done nothing for the last three weeks but deal with angry customers.”

“We’re seeing some trees doing O.K. with just the tips getting brown, and others are completely dead and it looks like someone took a flamethrower to them,” Mr. Coats said.

So far, the herbicide seems to affect trees with shallow root systems, including willow, poplars and conifers, he said.

Underwood Nursery is replacing the trees, which its liability insurance covers, but faces a $500 deductible for each incident. “It’s already cost us $150,000,” Mr. Coats said. Some landscapers are finding that their insurance does not cover the tree deaths at all.

The chemical name of the product is aminocyclopyrachlor, one of a new class of herbicides that has been viewed as safer than earlier weed killers.

DuPont, landscapers and others had high hopes for the product. It has low toxicity to mammals, works at low concentrations and can kill weeds that other herbicides have trouble vanquishing like ground ivy, henbit and wild violets. It works on the weeds’ roots as well as their leaves. No firm estimate exists on the extent of the tree die-off. But Bert Cregg, an associate professor of horticulture and forestry and an extension specialist with Michigan State University who has fielded many calls from landscapers and inspected affected trees, said the problem exists across the country. Many extension services have issued warnings, Dr. Cregg said.

“This is going to be a large-scale problem, affecting hundreds of thousands of trees if not more,” he said. Imprelis is used on athletic fields and cemeteries as well as on private lawns and golf courses, he noted.

Losing some of the biggest
While landscapers are replacing some of the trees, they cannot replace large mature ones, meaning that some homeowners have lost some of their biggest and oldest trees.

“I’m very concerned,” said Amy Frankmann, executive director of the Michigan Nursery and Landscape Association, who has heard from many members and who says the disaster could threaten the livelihood of landscapers whose insurance will not cover the cost. “Absolutely. One member is looking at having to replace a thousand trees.”

Mark Utendorf, owner of Emerald Lawn Care in Arlington, Heights, Ill., has seen dozens of customers’ trees turn brown. “It’s unfortunate because the product works exceedingly well on turf,” he said. “It kills creeping Charlie, and that’s something that’s very hard to kill,” Mr. Utendorf said, referring to a type of ivy that has been known to take over lawns.

He noted that the product had been viewed as part of a more environmentally safe lawn industry and a game changer. “I hope people will give DuPont a chance to make this product work,” Mr. Utendorf said. He added that he was still using it, though very carefully and not where there were conifers.

Imprelis went through some 400 trials, including tests on conifers, and performed without problems, according to experts at DuPont and at the E.P.A. The agency reviewed the herbicide for 23 months, which is standard procedure.

Even if the product is eventually proved to be a tree killer, it is considered unlikely that the E.P.A. would ban it, experts said. The agency would probably work with DuPont to change the herbicide’s labeling or to mandate larger buffer zones, they added.

Compost gets tainted
The United States Composting Council, meanwhile, warned in May that grass clippings from lawns treated with Imprelis should not be composted because the chemical survives the process and can kill flowers and vegetables that are treated with the compost. That warning is included on the Imprelis product label.

Dr. Cregg, the extension service specialist at Michigan State University, said it was possible that many of the affected trees could recover if they are left in place for a year to a few years, even if damage appears severe, because he has seen such a turnaround after similar damage to trees. “A lot of it comes down to the homeowner’s tolerance,” he said. “How long can they stand to look at this thing in the yard?”

Janet and Robert DaPrato of Columbus, Ohio, are facing that question as they gaze upon a 10-foot-high Norway spruce that started withering a month after a worker applied Imprelis in their yard. Then the needles fell off.

“The tree looks pretty well dead,” Mr. DaPrato said.

This article, "New Herbicide Suspected in Tree Deaths," first appeared in The New York Times.

Copyright © 2013 The New York Times


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