Paul D. Blanc M.D., M.S.P.H.

Household Hazards

Spare That Tree!

New herbicide linked to tree death

Posted Jul 25, 2011

As far as brand names go, Imprelis is an iconic choice. It subliminally suggests an archaic order of noble rank, perhaps one of the players on Game of Thrones. Just as in the cable TV series about cutthroat imperials, however, it seems like you don't want this character paying a visit to your manor house. Imprelis is a new, purportedly "eco-friendly" landscaping herbicide linked to an emerging horticultural holocaust.

The DuPont chemical moniker for the product's active ingredient is "aptexor." Since this alternative name invokes some sort of aggressive dinosaur species, it makes sense that the company would have gone for something else on its label. Worse yet, the chemical's generic formula name is a real mouthful: "aminocyclopyrachlor." As reported in the New York Times July 15, Imprelis (aka aptexor, aka aminocyclopyrachlor) has been implicated in the death of thousands of trees across the country. Others do survive, depending of course on how much of their foliage turns deadly brown, or, as one nursery worker was quoted as saying, looking as if someone had taken a flamethrower to the trees (

The new herbicide has been promoted for landscaping use on lawn-covered areas. The trees around golf courses have suffered particularly, but so too have those of private residences. The trees most at risk are noted to be shallow-rooted types, but the length of the hit-list is hardly reassuring, including willow, spruce, pine, and poplar. Imprelis is touted as the first herbicide in an entirely new class. In fact, its mode of action is believed to be very much in the same vein as most of the other chemical herbicides on the market. It kills its victims by operating through plant growth pathways that are governed by a class of natural hormones called "auxins." The synthetic herbicides that exploit this internal weapon, a foliage-blighting Fifth Column causing plant death through overstimulation, are referred to as "superauxins". The ideal herbicide is one that acts this way selectively, killing some plant types while sparing others. The Imprelis episode reminds us, in case we had forgotten, that we do not live in an ideal world.

So far DuPont, in a "Dear Turf Management Professional" letter, has only urged backing off on applications of its product near Norway spruce or white pine, since these are the trees involved in "a majority of reports" In a subtle eco-twist, DuPont seems to lay the blame not on its product, but rather on global warming: "In many geographies, environmental conditions over the past few years have stressed trees, particularly spruces. We have observed unfavorable symptoms in trees on properties that have not been treated with a herbicide. Good growing conditions and appropriate care to minimize stress will enable many trees experiencing signs of stress to recover and return to good health." It's a lovely riff on Reagan's "blame the trees" theme, suggesting that Spruce Stress is the next big thing, sort of the forest counterpart to PTSD  (

One line of defense that the trees do have is the U.S. EPA, which is required to review applicant pesticides before approval and to follow-up its decisions in case new information emerges suggesting a product should not stay on the market. The EPA only approved Imprelis last fall. According to various news reports, the EPA held a teleconference with various state agriculture officials July 6 to discuss the problem. The New York Times quoted an unnamed spokesman at the Agency as saying, "The E.PA. is taking this very seriously." United Press International, in a wire story days before the Times piece, quoted Kate Childress (identified as a DuPont spokeswoman) saying, "We're taking this seriously." Meanwhile, the only government source documenting that the EPA teleconference actually took place is the Department of Homeland Security "Daily Open Source Infrastructure Report" ( It's reassuring that everyone is so serious - even Homeland Security is tracking this story.

There is one silver lining. California, which has its own pesticide review process over and above that of the Federal EPA, hasn't approved Imprelis, at least so far. Unfortunately, that State's recent recommendation to proceed with a dangerous and controversial agricultural fumigant, methyl iodide, after having been a hold-out in the face of an earlier EPA go-ahead for that product, puts a dark tarnish on the silver. It's not the woodman's axe we have to fear, but the regulator's lapse.

About the Author

Paul D. Blanc, M.D., M.S.P.H., is a professor of medicine and the endowed chair in Occupational and Environmental Medicine at the University of California San Francisco.

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