Herbicide application

Herbicide application during invasive plant management at Mississippi Sandhill Crane National Wildlife Refuge.

Herbicides have been widely used on public lands in North America to kill non-native and invasive plants for decades. But a new report raises serious questions about whether taxpayers are footing a significant bill for a widespread but not widely known land management practice that may be causing more harm than good.

A pair of researchers at the University of Montana recently contributed to a new study that has found a lack of government data and accountability on whether this method is actually destroying “non-target” species and ecosystems and possibly allowing more destructive invasive species to take root.

UM researchers Cara Nelson and Viktoria Wagner, along with two Canadian researchers, surveyed government agencies and ag statistics companies in the U.S., Canada and Mexico and recently published their findings in the Journal of Applied Ecology.

They found that in 2010, 1.2 million acres of U.S. federal and tribal wildlands –an area the size of 930,630 football fields – was sprayed with 200 tons of herbicide. By far the most commonly used active ingredient was glyphosate –most commonly known to consumers under the brand name Roundup – which is a nonselective herbicide that also kills native grasses and herbs. Glyphosate is used in much higher concentrations on croplands, especially since the patent for the chemical expired in 2000 and its price dropped. However, because wildlands have higher biological complexity, they could be disproportionately sensitive to herbicide applications compared to crop-production ecosystems.

“The numbers are much less than those for croplands, but they are astonishing,” said Wagner, a former UM postdoctoral researcher who led the study.

The study found that the governments of Canada and Mexico kept no archived database of herbicide usage in invasive plant management – something Nelson said was surprising.


In the U.S., five out of seven contacted agencies tracked herbicide usage, and only four of those shared the data: The Bureau of Indian Affairs, the Bureau of Land Management, the Fish and Wildlife Service and the National Park Service.

The U.S. Forest Service, which oversees 193 million acres in the U.S. – a quarter of all federal lands – declined to share its data on herbicide use. Mike Ielmini, the Forest Service’s National Invasive Species Program Manager, told the researchers that he had concerns about his agency’s data quality. Ielmini did not return a call seeking comment on Tuesday.

In 2013, the Forest Service applied about 21,452 gallons of various herbicides in Montana, Idaho, South Dakota, North Dakota, Colorado, Nebraska, Wyoming and Kansas.

The report found that even the agencies that did share data did not consistently archive information on the effectiveness of the herbicide usage and its costs or make it publicly available.

“We were surprised that we could not obtain a full accounting of herbicide usage for natural areas management in the U.S. and that no data were available for Canada,” Nelson said. “And it hasn’t gotten a lot of attention in the press.”

Nelson, a botanist and an associate professor in UM’s Department of Ecosystems and Conservation Science, said that herbicides can play an important role in removing destructive invasive plants in natural areas.

“However, they can also have substantial downsides, including the potential to further degrade ecosystems by reducing germination and establishment of native plants and facilitating secondary invasion by weeds,” she explained. “Although herbicides may kill target weeds, if native plants don’t establish after spraying, there is a high probability that undesirable plants will colonize and these so-called ‘secondary invaders’ can have even more detrimental impacts than the plant that was the initial target for control. A common secondary invader in the west is cheatgrass (Bromus tectorum), which is one of the invaders that has the most severe effects on wildlife habitat and ecosystem function.”


According to the Montana Weed Control Association, exotic weeds such as spotted knapweed and leafy spurge infest nearly 7.6 million acres of land in Montana, and the state spends more than $42 million every year on the direct and indirect costs of knapweed species. There is no question that invasive plants are a problem, and that herbicides can be an effective solution to that problem. However, Nelson argues that more oversight is needed to ensure taxpayer dollars are being used wisely.

“The real story is about what this means for 21st century approaches to ecological restoration and herbicides as a tool for ecosystem repair,” she explained. “Ecological restoration – the process of repair of ecosystems that are damaged, degraded, or destroyed – is now a multi-trillion dollar a year industry. Given this large financial investment, it is essential to ensure that restoration practices have their intended effect and in order to do that, it is necessary to monitor treatment outcomes.”

Nelson is quick to point out that she and her colleagues are not advocating that herbicides should never be used.

“Rather, in order to use herbicides as a tool for managing natural areas most effectively, we need to monitor how and when they’re working,” she said. “We can apply the lessons learned to improve our ability to repair ecosystems, otherwise we may be spending this money and wishing later, when we see the effect, that we hadn’t taken management action. This applies to many of the types of restoration that we do.”

Nelson said that the city of Missoula’s Parks and Recreation Department is doing an excellent job of monitoring its herbicide usage. Morgan Valliant, the city’s conservation lands manager, is working with Nelson’s lab at UM on studies to control invasive plants and on the herbicide impacts on native plants.

However, Nelson said that many herbicide applicators in Montana use a chemical called aminopyralid, a selective herbicide, because its use doesn’t require a license.


There have been only eight published studies on the efficacy of aminopyralid, and Nelson said the methodology used in some of those studies is highly suspect because they didn’t use a “control” to contrast the herbicide application with a natural area that hadn’t been sprayed.

The bottom line, according to Nelson, is that it’s important to ensure that restoration practices have the intended effect, and to do that the government needs to be monitoring treatment outcomes.

“Government agencies to date have not done enough monitoring to ensure that we are using herbicides in the most effective way possible and avoiding non-target effects,” she said.

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