Herbicide killing pine trees

A new herbicide may be taking the green out of many evergreens.

Thousands of eastern white pines and Norway spruces across the country began dying and showing damage this year, and a key suspect in the mystery is Imprelis, a weed killer many lawn companies and landscapers started using this spring.

Chris Starbuck, a University of Missouri Extension state woody ornamentals specialist, said this problem will leave holes in many landscapes.

"Every tip on this tree is affected, and to produce new growth it would have to produce new shoots from the two-year growth, so it's not likely this tree will recover," Starbuck said as he surveyed damage to white pines in a Columbia lawn. "It's been a surprise to everyone involved how extensive the damage appears to be. I think there will be lots of trees that have to be replaced in landscapes and it's going to cost somebody some money."

Professionals started using Imprelis this spring for the first time.

Many progressive lawn care companies gravitated toward it because it is highly effective at controlling common yard pests like dandelion, clover and ground ivy. It also boasted a low use rate – only four ounces per acre – while being less toxic to mammals. Consumers cannot buy the product themselves, so it is only a problem in lawns treated by professionals.

Gene Hrdina, owner of Columbia-based Designer Landscape, said a high percentage of his clients' white pine and Norway spruce show damage.

"My clients are upset, I'm upset, and it's unfortunate for DuPont, our clients and other applicators," said Hrdina, who has been in business for 27 years. "It's going to leave a mark. A lot of landscape contractors and lawn care applicators will likely lose clients."

Reports of tree damage come from Illinois, Indiana, New Jersey, Ohio, Pennsylvania and other states. Imprelis is registered for use in all states except New York and California. DuPont alerted professionals of the problem after symptoms began surfacing toward the end of May. It advises them not to use the herbicide near white pine or Norway spruce.

While conifers show the most extreme damage, Imprelis has apparently caused damage symptoms on other trees and shrubs. That burn manifests in twisted branch tips, distorted growth, cupping of leaves, and the browning of leaves and needles in extreme cases.

Starbuck noted that damage to plants ranges widely even within a single landscape, with one pine tree showing few symptoms and another 10 feet away showing browned needles and twisted branch tips. Older conifers are hit particularly hard because their root systems spread shallowly out more than 50 feet into most lawns.

Since Imprelis works not only by leaf and stem contact but also through root uptake, the shallow roots seem to make evergreens more vulnerable.

"Imprelis is a whole new chemistry," Starbuck said. "We've been used to using broadleaf herbicides that are safe to apply right up to the trunk of the tree, but in this situation the chemical moves through the soil to be taken up by roots of weeds, and apparently by shrubs and trees as well."

No one really knows why some plants are hit harder than others, even within a given species. Some theorize that other environmental factors such as irregular rain patterns or high heat are causing symptoms to show this year.

Since Imprelis lingers in the soil for more than 50 days, some think the situation will get worse before it improves. DuPont asks professionals and homeowners to help track symptoms by reporting damage to their lawn care providers and leaving damaged trees standing in their landscapes for a full year. Do not mulch dead trees or send them to your cities landfill because herbicide residue in the tissue may cause the mulch to inhibit plant growth.

"I encourage homeowners to work closely with their lawn care providers and operators to work with insurance companies and DuPont about damaged trees," Starbuck said. "Not every symptom, every brown leaf on a tree, should be attributed to Imprelis. In many cases you'll find Imprelis was not applied."

Hrdina has contacted all his clients, and DuPont representatives have already visited to survey damage at some of his sites. He's unsure of what will become of these trees.

"My belief is that a lot of these trees will continue to be damaged. Once the two-year needles fall off they won't be able to photosynthesize because the new branch tips are burned on these trees," he said. "I think everyone will be more on guard and be very cautious about new products until they are tested in the field and have some time under their belts."

Pines and spruces that died will be hard to replace.

"In many situations, losing a large evergreen tree in your landscape leaves a huge hole and many will never be able to replace that tree in their lifetimes," Starbuck said. "It takes a long time for trees to gain that size, so it really is heartbreaking to a lot of homeowners to have this situation."

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