Imprelis and the continuing fall out

The Imprelis herbicide has been national news this year.  A new weed control product released by DuPont this past spring showed great promise in managing difficult to control weeds with lower amounts of herbicide.  However, after trees began showing signs of damage and dying off this spring it appeared that Imprelis was the culprit. 

It is important to know that Lawn Lad never purchased or used Imprelis in our operations. While we are always looking for and testing new processes and products to use in our operations to provide the best possible results - we are reluctant to be the first to test new products for this very reason.  You can rest assured that we did not spray this product on your property. 

For more information about Imprelis here is an article from the Ohio State University Extension newsletter - The Buckeye Yard & Garden Line from September 1, 2011. 

IMPRELIS UPDATE. An ongoing saga this year is a self-inflicted wound, an iatrogenic agent, so to speak, that has affected every corner of the green industry and their customers. An "iatrogenic agent", borrowed from medical terminology, is something which intended for positive use, ends up with a negative effect. The cure that creates another crime - a side effect. The case study we are all living this year is of Imprelis, a weed - killer, an herbicide developed by DuPont. This herbicide was used commercially for the first time this spring for a variety of turfgrass applications. It was widely touted as a low volume herbicide for broadleaved weeds, including many tough to control weeds such as violets. It was touted as being very effective for these weeds, AND it was! It was touted as having low environmental danger because it did not have the tendency to volatilize (turn into a gas during hot weather) and move off-site to unintended plants; the US EPA touted this as a plus. Many of the better-informed green industry companies, in good faith, with a labeled product, added Imprelis to their programs for this year.

Imprelis was indeed effective for these weeds. Unfortunately, unintended consequences did emerge. After initial applications in April, starting in late May and early June, lawn care companies and their customers, golf course professionals, and professionals taking care of turfgrass in commercial sites began noticing problems, not on the turfgrass (and weed control was excellent) but on certain adjacent trees. Most noticeably affected were evergreens such as Norway spruces, white pines, other needled conifers, and in some cases deciduous trees such as honeylocust.

There were comments on the Imprelis label about not applying the chemical on exposed roots of trees and of not using grass clippings from treated areas as mulch. However, for unanticipated reasons, off-site damage of certain trees occurred in a number of cases. Not always, in fact the vast majority of Imprelis applications resulted in no damage to adjacent trees. Trees do have extensive root systems, though, that as the tree grows, roots extend well beyond the dripline, and we did have many major storms with localized flooding, and it turns out that, though volatility of the chemical was low, root uptake appeared to be a major problem for certain trees.

So, for example on Norway spruce, we began to notice browning and curling of new shoots, browning and twisting of needles, sometimes browning of entire trees. Often there was still green tissue in the buds, so there was hope for recovery. The extent of damage varied greatly, sometimes occurring on some trees in a line but not all, even though clearly, as noted by weed control in the turfgrass, the application of the herbicide was uniform. The particular geography of the tree root system into the turf area was clearly a factor. The vascular (water and nutrient conducting) system of spruces and pines was a tip-off to the root uptake aspect of this problem. Unlike many plants, a spruce's vascular system ascends spirally up the tree, and when browning and twisting on a tree was not throughout, you could see the pattern of damage in a tell-tale spiral pattern, indicating root uptake.

As the problem emerged, the green industry, DuPont, regulatory agencies, the media and the general public have become more and more aware of this issue. Ultimately, Imprelis sales were suspended, and incredibly we are now even hearing the "b" word relative to damages, as in over a billion dollars in injury to Norway spruces and other plants nationwide. Litigation looms. We are now all looking at how this happened and the answers to questions that will allow us to learn from this episode. Was it a perfect storm of unanticipated movement of the chemical in runoff water due to the flooding caused by many major storms this spring? Can science better test prior to registration the potential for this happening? What is common about the growth processes and uptake potentials of the most sensitive tree species that resulted in such differential damage? What is the nature of this particular chemistry that made the industry vulnerable to this problem? How can we prove through residue analysis whether Imprelis damage caused problems on a particular tree? What is the prognosis for affected trees?

The tough truth is that it takes time to answer these questions, including one key bottom line of what to do now with affected trees. Clearly there is a range of injury to trees and many will recover. Others were badly affected and will not recover. Others will survive, but with the extent of damage may be "horticulturally dead" in that after pruning out damaged branches will no longer serve the ornamental or windbreak function desired by the customer. Getting rid of the chemical quickly in the soil is problematical. Early on, some companies tried to water extensively to try to leach the chemical out of the root zone. At least in some cases this resulted in greater damage as this presumably resulted in moving chemical to other roots. The chemical is not particularly short-lived. DuPont has advised not replanting into the site of a removed tree until October where Imprelis was applied prior to June of this year, not replanting until November if applications were made in June.

One thing is certain: communicate with affected customers and your connections in the green industry and with DuPont and insurers. Sustain that communication. Take pictures of the damage sequentially. Hone your diagnostic skills. Many cases of white pine weevil insect damage and Diplodia tip blight fungal disease and long-term root health problems on spruce and pine were misdiagnosed as Imprelis damage this season. Monitor plant development this fall and next spring as you consider whether or not trees must be pruned or replaced.

To learn more, here is one good reference for starters:

"A Turf Professional's Guide to Suspected Imprelis Herbicide Injury in Your Landscape"