Wehr loses 300 trees to herbicide application mistake
Two acres killed off in effort to remove invasive ground flower
More than 300 hardwood trees at the Wehr Nature Center died after a weedkiller was sprayed in the woods, and Milwaukee County Parks staff will be cutting the trees this winter as the first step in restoring the land, officials said.
Visitors see the dead canopy of the woods as soon as they drive into the center’s parking lot off College Avenue in Franklin. The leafless treetops extend across two acres east and south of the visitor center as testament to using the wrong tool for a job.
Yellow ribbons mark mature black walnut, sugar maple and ash trees to be logged this winter by Parks
Department foresters. A few of the dead trees will remain standing for wildlife habitat.
Brian Russart of the Milwaukee County Parks Department said the incident was “a learning lesson” for parks staff. That pesticide will be used in the future to control invasive weeds only where there are no trees, he said.
Park staff applied a weedkiller, Polaris AQ, to the leaves of a nuisance, invasive plant — Lesser celandine — in April 2017, said Brian Russart, natural areas coordinator for the parks department.
Polaris contains the chemical Imazpyr and it did the job effectively. Within a few weeks, parks staff noted the unwanted celandine was dead.
But a month later, Wehr staff observed the hardwood trees were not growing leaves. They were dying. And they did not leaf out this spring.
“Polaris removed the celandine but killed the forest we were trying to save,” Wehr staff wrote in the Fall 2018 “Wehr Words“newsletter.
There is disagreement among parks department staff on whether the herbicide should have been sprayed in the woods.
Russart said there were no “red flags” on the pesticide’s label that would have ruled out its use. “There was no glaring failure,” he said.
“We regularly use herbicides to control invasive species and this was the first time this happened,” he said.
But Wehr staff, in the newsletter article, “Forest of Unintended Consequences,” said the label “cautions users about applying near desirable trees.” The reason for the caution is that it can be taken up by shallow roots and flow through a tree.
Wehr staff described the incident as a “bull in a china shop” moment of humans creating abrupt change in a natural environment “that leaves more broken pieces than nature can glue back together quickly.”
The woods closest to the visitor center had been dominated by black walnut. About 25% of the trees are ash and they already had been impacted by the Emerald ash borer, a destructive insect pest, according to Russart.
Russart said the incident was “a learning lesson” for parks staff. That pesticide will be used in the future to control invasive weeds only where there are no trees, he said.
Briana Frank, owner of Tree Health Management LLC in Madison and a consulting arborist, said she receives calls about unintentional damage caused by use of herbicides but not any of such a large scale at just one location.
Donna Gilson, a spokeswoman for the state Department of Agriculture, Trade and Consumer Protection, said Friday that the county parks staff had contacted the department’s pesticide regulators this year about the incident.
“This was not misuse, in legal terms, since it was applied according to the label,” Gilson said. “It was unfortunate.”
Such large-scale unintended damage caused by herbicides does happen occasionally in Wisconsin, she said.
Restoration of the forest
Squirrels and deer, including a few bucks, walked through the herbicidescarred landscape on Friday. There are scattered bare patches of soil beneath the dead trees where no plants grew this summer, not even garlic mustard, a nuisance invasive weed.
Parks department staff will attempt to sell black walnut and maple lumber from the logging this winter to generate revenue.
Next spring and summer, staff will monitor and control invasive weeds before preparing the soil for planting new trees, shrubs and wildflowers.
“We’ll plan a climate change forest with southern species of trees that might move up here over the next 100 years” due to warming weather patterns, Russart said. Among those tree species are American sycamore and hackberry.
And parks staff will plant native trees, such as white and bur oak, that likely will put up with a warming climate and stick around here, he said.
“We’ll have a greater diversity of trees here,” Russart said.
Lesser celandine was brought to the U.S. from Eurasia for its showy, ornamental flowers. It is now prohibited in Wisconsin.
This alien forms a rapidly spreading ground cover with daisy-like, glossy yellow flowers and kidney-shaped to heart-shaped leaves, according to the Wisconsin Department of Natural Resources.
It gained a toe-hold at Wehr 10 years ago and eventually forced out native plants and flowers in up to one-third of the woods near the visitor center and was spreading outward.
Digging it up and spraying it with the Rodeo brand weedkiller containing glyphosate did not stop its spread, parks staff said. So workers selected Polaris AQ to stop it.
Dead hardwood trees unintentionally killed by use of a herbicide at Wehr Nature Center are marked for logging this winter. More photos at jsonline.com.