Avoid use of herbicide Imprelis, Purdue experts advise

July 22, 2011

This photo, taken in mid-July on the grounds of the Purdue Federal Credit Union in West Lafayette, Ind., shows a damaged locust tree in the foreground and a damaged Norway spruce in the background. The Office of Indiana State Chemist is investigating complaints of injury to trees, shrubs and other ornamental plants following the application of the herbicide Imprelis, which is a suspected cause. The investigation is not yet complete. (Office of Indiana State Chemist photo)

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WEST LAFAYETTE, Ind. – Lawn care providers should not use the herbicide Imprelis on residential and other properties such as golf courses as experts try to determine whether it is injuring trees and ornamental plants and can be used safely, a team of Purdue University specialists advises.

The team released a guide Friday (July 22) for turfgrass professionals, and the Office of Indiana State Chemist distributed information to them on the process for investigations into complaints about injury to trees and shrubs.

The herbicide is suspected of injuring mainly evergreens, including Norway spruce, Colorado blue spruce, arborvitae and eastern white pine. Symptoms of injury also have been noted on honeylocust and several other types of trees and ornamental plants.

So far, Extension services in 22 states from Kansas to Pennsylvania, including Indiana, have reported cases of injury possibly associated with Imprelis.

"At this point we are recommending that applicators do not use Imprelis on residential properties or other properties that have trees, shrubs and other ornamentals until we can learn more about how to safely use this herbicide," said the team's leader Aaron Patton, an assistant professor of agronomy and turfgrass Extension specialist. "However, sod farms, athletic fields and large commercial properties without trees and ornamentals should be able to safely use this product for effective weed control in the meantime."

He and three others with expertise in horticulture and plant disease diagnostics and pathology wrote "A Guide for Turf Professionals on Suspected Imprelis Herbicide Injury in the Landscape," with portions adapted from a Michigan State University document. The guide is available online at http://www.ppdl.purdue.edu/PPDL/pubs/briefs/ImprelisLCO.pdf

Purdue faculty and staff also produced a publication that answers commonly asked questions from homeowners about Imprelis. It is available at http://www.ppdl.purdue.edu/PPDL/pubs/briefs/ImprelisFAQ.pdf

Imprelis, with the active ingredient aminocyclopyrachlor, was approved late last year for use by lawn care companies and other professionals. It is intended to control a variety of broadleaf weeds, such as ground ivy (creeping Charlie) and wild violet, in lawns, golf courses, parks, cemeteries, athletic fields and sod farms.

Made by DuPont, reported use of Imprelis in Indiana occurred primarily from March to June. 

Injury symptoms include brown shoots and needles and twisted and stunted shoots, especially near treetops. Symptoms have been most severe on current-year growth, which means that the greatest degree of injury can be seen in young trees and in the tops of older trees.

Field investigators with the Office of Indiana State Chemist, based at Purdue, have been spending nearly all of their time looking into about 150 complaints since the office received its first inquiry in early June. 

Investigators are getting to sites of complaints as quickly as possible to collect evidence. Because of the large number of complaints received in a relatively short period, processing of investigations will be slowed somewhat, according to the state chemist's office.

"Credible investigations take time to process," the office wrote in its statement to pesticide application businesses. "However, OISC is aware of the heightened interest by both consumers and licensed applicators and is working diligently to expedite results wherever possible." 

While awaiting results, homeowners should continue to monitor plant injury to determine if it worsens or improves, the statement said. They should document any changes with photographs.

Homeowners with trees and other plants showing symptoms of injury should contact their lawn care service provider to ask if Imprelis was applied. If so, they should get information from the applicator stating when and how much Imprelis was used.

The Plant and Pest Diagnostic Laboratory at Purdue in recent weeks has received many samples of trees and other ornamentals from homeowners and professionals who suspect injury from Imprelis. The PPDL can evaluate the sample for disease and insect problems, but it does not offer analysis of plants or soil for herbicide or other chemical residue. Such analysis is performed by the state chemist's office, and official investigations must begin there.

Lawn care companies wanting the OISC to investigate symptoms on trees and shrubs that might have been caused by an application of Imprelis should contact George Saxton at 765-494-1582, saxtong@purdue.edu. Homeowners can file a complaint directly with the OISC if the lawn care operator confirmed that Imprelis was applied, has visited the site and agrees there is injury.

Homeowners not using a lawn care service but experiencing the plant injury symptoms can contact the OISC directly at 1-800-893-6637.

Imprelis was registered by the U.S. Environmental Protection Agency and the OISC in the fourth quarter of 2010. The EPA approved its use in part because of its relatively low toxicity to people and animals.

"There is no evidence to suggest that Imprelis is harmful to people or pets," the OISC said.

New information about the degree and extent of the problem will be posted online on the following websites as it becomes available:

* Plant and Pest Diagnostic Laboratory: http://ppdl.purdue.edu/PPDL

* Purdue Turfgrass Program and blog: http://www.agry.purdue.edu/turf  and http://purdueturftips.blogspot.com

* Office of Indiana State Chemist: http://www.isco.purdue.edu

Writer:  Keith Robinson, 765-494-2722, robins89@purdue.edu

Sources: Aaron J. Patton, 765-494-9737, ajpatton@purdue.edu

                 Dave Scott, pesticide administrator, Office of Indiana State Chemist, 765-494-1593, scottde@purdue.edu

                 Tom Creswell, director, Plant and Pest Diagnostic Laboratory, 765-494-8081, creswell@purdue.edu

Ag Communications: (765) 494-2722;
Keith Robinson, robins89@purdue.edu
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