An herbicide thought to be environmentally friendly has become the leading suspect in the deaths of spruce and pine trees across the country, according to The New York Times. Made by DuPont the herbicide, called Imprelis, was conditionally approved for sale last fall by the Environmental Protection Agency. But reports of dying trees started cropping up this spring and now DuPont has started an investigation.

Approved for use in every state but New York and California, Imprelis is used by landscapers and golf course groundskeepers to control a variety of weeds including dandelions, clover, ground ivy and wild violets, among others. But in June DuPont wrote a letter to “turf management professionals” that said, “Some of your industry colleagues have reported observing various unfavorable symptoms on certain species of trees and we wanted to keep you informed.”

The trees most commonly affected, according to DuPont, are Norway Spruce and White Pine. As a precaution, DuPont is asking landscapers not to use Imprelis “where Norway Spruce or White Pine are present on, or in close proximity to, the property to be treated.”

“It’s been devastating,” Matt Coats, service manager for Underwood Nursery in Adrian, Mich. told the New York Times. “We’re seeing some trees doing okay with just the tips getting brown, and others are completely dead and it looks like someone took a flamethrower to them.”

This is not the first alert that DuPont has issued about Imprelis. In March, DuPont cautioned: "The product label requires that you do not use grass clippings from areas treated with Imprelis for mulching or compost, or allow for collection to composting facilities. Grass clippings must either be left on the treated area, or, if allowed by local yard waste regulations, disposed of in the trash."

Imprelis is a post-emergent herbicide, which means it kills growing weeds. Pre-emergent herbicides kill germinating weed seeds. Before applying any herbicide you should identify the type of weed you’re trying to control. Lawn weeds are either annual or perennial grass weeds or broadleaf weeds. Grass weeds, such as crabgrass, have parallel leaf veins, while broadleaf weeds, such as dandelions, have branched veins. For more information, see our Guide to common weeds and lawn problems.