Monsanto's signature herbicide glyphosate, more commonly known as Roundup, is by far the most widely used weed killer in the world, according to a report published this week.

Glyphosate was first sold commercially in 1974, but farmers used comparatively little of it because it killed both weeds and crops. But Monsanto and other seed companies genetically engineered cotton, corn and soybeans to be resistant to the herbicide, and sales took off in the mid-1990s.

The report, published in the peer-reviewed journal Environmental Sciences Europe, says that glyphosate use by U.S. farmers shot up from 12.5 million pounds in 1995 to 250 million pounds in 2014, a 20-fold increase, and its total use globally rose from 112 million pounds in 1995 to 1.65 billion pounds in 2014.

Despite its popularity, researchers have questioned whether the chemical contributes to public health and environmental problems. Last year, a World Health Organization panel classified the weed killer as "probably carcinogenic to humans," and the state of California has proposed to list glyphosate as a known human carcinogen under state law.

Industry has challenged those decisions, and has steadfastly contended that use of the weed killer has been proven safe in dozens of studies and by two decades of widespread use. Concern is also growing that overuse of glyphosate has caused weed species in some areas to become increasingly resistant to it.

"Glyphosate will likely remain the most widely applied pesticide worldwide for years to come, and interest will grow in quantifying ecological and human health impacts," the paper concludes. The research is available on the website of Environmental Sciences Europe.