Imprelis – The Herbicide That Keeps On Giving

Imprelis, marketed by DuPont as an environmentally safe alternative to 2,4-D, has shown itself to be anything but. More than two years after its ban by the EPA, it’s still damaging trees.


At one location, for example, blue spruce trees had no Imprelis symptoms in June of 2011, some bud death in spring of 2012, and now these blue spruce appear to be dying in 2013. – Purdue Extension


eastern white pine imprelis damage

Imprelis damage continues to show up in pine trees. This sample from an eastern white pine was sent to Michigan State researchers in spring, 2013

In 2011, landscaping companies started applying DuPont’s new herbicide Imprelis to lawns all over the U.S. Imprelis – with the active ingredient aminocyclopyrachlor – was marketed by DuPont to control broadleaf weeds such as ivy in established turf.

Shortly after application, homeowners and golf courses started reporting significant damage and die-offs of trees and ornamentals adjacent to the treated lawns. Most affected were spruce and pine trees, but eventually damage was also confirmed in Japanese yew, eastern white cedar, arborvitae, boxwood, lilacs, honeylocust, maple, ginkgo, privet, willow, and others.

In states where trees were damaged by Imprelis, university researchers worked with state chemists and other scientists to confirm that the herbicide did indeed cause the reported damage. In August of 2011 the EPA banned the sale of Imprelis.

Damaged parties – landscapers, townships, counties, golf course owners, homeowners – were encouraged to file a claim with DuPont, and eventually over 34,000 claims were filed across the U.S., primarily in the upper midwest. Some have received settlements, some lawsuits are still pending. DuPont’s total bill will most likely exceed $700 million.

“I have seen whole quarter-mile rows of trees smoked by this,” says Mark Stennes, a plant pathologist in South St. Paul, Minnesota.  “this is absolutely the worst I have ever seen.”

Imprelis continues to injure trees

honeylocust damage

Galls formed on this honeylocust tree due to Imprelis damage

But the injuries to trees and shrubs continued to be reported in 2012 and even in 2013. This spring, educators at Michigan State University received images from a homeowner showing “club-like callus formation on terminal shoots of a pine exposed to Imprelis” (see picture above). Further complicating matters were the extreme weather events across the United States in 2012 – early spring heat, late frosts, drought, and extreme heat. These record weather events made it difficult for struggling trees and ornamentals to recover from the herbicide’s damage.

Soil testing by university laboratories has shown that Imprelis has broken down in the soil according to its published half-life (35-100 days), leaving little trace two years later. But scientists at Purdue University have discovered that the Imprelis stored in the tissues of damaged plants and trees has broken down much more slowly and may still be present in plant tissue.

Michigan State University Extension reported that  “their group … [found]… Imprelis residues in leachate from container-grown tomato plants that were mulched with ground branches from Imprelis-affected trees. The tomato plants also showed signs of abnormal growth. This information is important as Imprelis-related tree removals continue. Waste material from Imprelis-affected trees should be burned or landfilled, but not mulched.”


eastern white pine imprelis damage

Imprelis caused thickened shoot tips on this eastern white pine

What to do if your trees are damaged

If trees on your property were damaged by Imprelis, the soil around them should be free of the herbicide at this point – but have a soil test done to be sure of that. Many factors determine how quickly an herbicide breaks down – soil temperature, rainfall, bacteria, and sunlight among them. But with the extreme weather events the United States experienced in 2012, it’s not safe to assume that Imprelis broke down in your soil according to schedule.

If the trees were or will be removed, make sure that the infected debris comes nowhere near your garden or a public municipal mulch or compost site. It’s very likely that plants and trees damaged by Imprelis still have the herbicide in their tissues, and if it comes in contact with living plants, it may kill or damage them. The only responsible and safe way to dispose of imprelis-infected debris is to burn it or send it to a landfill.

If trees were damaged but not killed, they should recover. But it’s impossible to predict at what speed that will happen, since there are so many factors that influence their recovery: the amount of damage, the amount of Imprelis lingering in the soil near the trees, weather, soil conditions, and more.

To help your plants and trees recover, the Purdue Extension recommends that you prune back all dead or dying branches and tissues back to live material. This could take a season or two, since the herbicide is known to move through living plant tissue. They also recommend that you don’t fertilize any damaged trees, as trees under stress need to use all of their energy to recover, and processing nitrogen requires expending energy and transferring water from the roots.

Todd’s Google+ profile

About Todd Heft

Todd Heft is an organic gardener and freelance garden writer who lives in the Lehigh Valley, PA and has gardened for most of his life. When he isn't writing or reading about organic gardening, he's gardening. His first book, "Homegrown Tomatoes: The Step-By-Step Guide to Growing Delicious Organic Tomatoes In Your Garden" is available on Amazon now. Google
Tagged , , . Bookmark the permalink.

One Response to Imprelis – The Herbicide That Keeps On Giving

  1. ed says:

    The problem with replanting and assuming Imprelis has lessened in the soil is the fact that any roots remaining from the damaged plant that was removed can still be in the ground unless many square yards are excavated around where the tree was. Tests have shown Imprelis still in plant tissue, so unless you’re successful in removing ALL plant tissue including all roots than replanting is risky. Roots from trees can be many many yards away from the center of the tree trunk making excavation and full removal of all plant tissue very costly and that’s why some have opted out of the class settlement since it didn’t not allocate enough money for a full excavation of ALL plant tissue including roots that may extand under driveways, patios and other hardscapes or even way out under a lawn. No one can for certain know when it truly is safe to replant in order for the new plant to grow normally without any Imprelis impact.