A Swiss chemist working for a pharmaceutical company, Dr. Henri Martin, discovered glyphosate [N-(phosphonomethyl) glycine] in 1950 . Because no pharmaceutical applications were identified, the molecule was sold to a series of other companies and samples were tested for a number of possible end uses. A Monsanto chemist, Dr. John Franz, identified the herbicidal activity of glyphosate in 1970, and a formulated end-use product called Roundup was first sold commercially by Monsanto in 1974 .
For two decades, the number and diversity of agricultural and non-farm uses grew steadily, but the volume sold was limited because glyphosate could only be sprayed where land managers wanted to kill all vegetation (e.g., between the rows in orchards and viticulture; industrial yards; and, train, pipeline, and powerline rights of way). Some applications were, and still are made after a crop is harvested, to control late-season weeds that escaped other
control measures. In some regions, desiccant applications are made late in the growing season to speed up harvest operations, especially in small grain crops.
In 1996, so-called “Roundup Ready” (RR), genetically engineered (GE) herbicide-tolerant (HT) soybean, maize, and cotton varieties were approved for planting in the U.S. This technological breakthrough made it possible to utilize glyphosate as a broadcast, post-emergence herbicide, thereby dramatically extending the time period during which glyphosate-based herbicides could be applied. Alfalfa and sugar beets engineered to tolerate glyphosate were first approved and commercially marketed in 2005 and 2008, respectively, but federal lawsuits citing procedural violations of the National Environmental Policy Act delayed full commercial sales until 2011 for RR alfalfa and 2012 for RR sugar beets [3, 4].
To quantify the environmental and human health impacts stemming from pesticide use, it is essential to know how much pesticide is being applied in a region on a given crop, collectively across all crops, and in other places (e.g., forests, rangeland, along rights-of-way, industrial yards). Ideally, data are available on the land area and crops treated; the timing and method of applications; rates and number of application; the formulation applied and the total volume applied per hectare. Unfortunately, all these data are rarely available.
Rising use heightens risk concerns. Growing reliance on the broad-spectrum herbicide glyphosate has triggered the spread of tolerant and resistant weeds in the U.S. and globally [5–10]. To combat weeds less sensitive to glyphosate, farmers typically increase glyphosate application rates and spray more often [11–13]. In addition, next-generation herbicide-tolerant crops are, or will soon be on the market genetically engineered to withstand the application of additional herbicides (up to over a dozen), including herbicides posing greater ecological, crop damage, and human health risks (e.g., 2,4-D and dicamba) .
This paper presents trends in glyphosate use in order to help researchers better understand and quantify the risks and benefits stemming from uses of glyphosate-based herbicides. Detailed data on trends in glyphosate use in the U.S., both in and outside the agricultural sector, are presented, while the data on global glyphosate use are less complete and more uncertain. Fortunately, sufficient data are available to track the impact of GE herbicide-tolerant (HT) crops on global glyphosate-based herbicide (GBH) use since 2010 [14–17].