Although the amount of herbicides used on croplands is reported and known, recent research reveals huge amounts of the plant-killing chemicals are used on public and tribal wildlands as well, according to a new study.

More than 1 million acres of federal and tribal lands were sprayed with chemicals to kill invasive plant species in 2010, a fact researchers said had not previously been known.

The chemicals have been developed to control weeds in croplands, but have been widely used against non-native plants that pose threats to federal wildlands. The concern, researchers said, is that it has largely gone unreported.

Researchers said gathering the data required many emails and phone calls to government offices and agro-statistical companies in the United States, Canada and Mexico.

"Well-designed studies on the efficacy and effects of herbicides on native plant communities, coupled with increased reporting of herbicide usage, would assist with developing best practices for effectively and safely using herbicides to manage non-native plants in wildlands," Cara Nelson, a researcher at the University of Montana, said in a press release.

For the study, published in the Journal of Applied Ecology, researchers requested data on amounts and areas sprayed, though they report the efficacy and financial costs of using the chemicals has not been recorded in a standardized and consistent manner, nor has data been publicized.

The study reveals about 1.2 million acres of federal and tribal land were sprayed with approximately 201 tons of herbicide, most of which contained the active ingredient glyphosate. The selection of glyphosate surprised the researchers, they say, because it is nonselective and harms both grasses and herbs, which can damage native plants.

The researchers suggest better tracking of amounts and costs of the chemicals, as well as studies on their effects against non-native plants and the native ones the agencies are attempting to protect.

"The numbers are much less than those for croplands, but they are astonishing," said Wagner, a former UM postdoctoral researcher who led the study. "Imagine: The wildland area sprayed by herbicides in that year is comparable to 930,630 football fields, and the amount of herbicides used equals the weight of 13 school buses."