The United States Department for Aguriculture's Animal and Plant Health Inspection Service (APHIS) announced on Friday that it will delay approval of new varieties of herbicide-resistant genetically modified crops created by two US-based agribusinesses, pending environmental assessments.

The crops, produced by Monsanto and Dow and engineered to be resistant to controversial older herbicides 2,4-D and dicamba, were engineered in response to the threat of 'superweeds' which tolerate applications of glyphosate (sold by Monsanto as Roundup), and are now present in at least thirteen US states, though their existence was initially denied by agrochemical manufacturers.

Release of the deeply divisive new seeds had been expected in time for planting in 2014, but Friday's announcement means this is now extremely unlikely. Instead, USDA will produce full environmental impact statements on the new products. This is a novel step for USDA, which has approved GM crop varities including alfalfa and sugar beet without conducting such analysis in the past (and has been subject to heavy criticism and litigation for so doing).

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The development of crops resistant to both roundup and older chemicals has alarmed even some mainstream agriculture stalwarts; researchers from Penn State University and the USDA's Agricultural Research Service (ARS) issued a resounding warning last year, in a paper that suggested, "Crops with stacked herbicide resistance are likely to increase the severity of resistant weeds… facilitate a significant increase in herbicide use [and] encourage continued neglect of public research and extension in integrated weed management."

The paper's authors advised "Agricultural weed management has become entrenched in a single tactic—herbicide-resistant crops—and needs greater emphasis on integrated practices that are sustainable over the long term."

In a statement on its website, APHIS announced that the agency will conduct two separate environmental impact statements on the crops (two varieties of soybeans and of maize, engineered to resist treatment with 2,4-D, and one variety each of soybean and cotton modified to tolerate applications of dicamba),  "to better inform decision-making regarding the regulatory status of [herbicide resistant] crops."

Opponents of the new seeds point out that their development runs contrary to industry claims that switching to genetically modified seeds will allow farmers to reduce their use of damaging chemicals. Research from last year suggests that this has not been the case; Professor Charles Benbrook, of Washington State University, found that herbicide use in the production of three genetically modified herbicide-tolerant crops (cotton, soybeans and corn) has increased, in direct contrast to industry claims.

Benbrook said his "counterintuitive finding is based on an exhaustive analysis of publicly available data from the U.S. Department of Agriculture's National Agriculture Statistics Service." The WSU professor found that the emergence of resistant crops strongly correlated with the upward trajectory in herbicide use. He estimated that, for farmers reliant on GM crops, resistant weeds are "driving up the volume of herbicide needed each year by about 25 percent."

Although herbicide resistance in weeds appears to be spreading - According to Dow, the acreage affected by herbicide-tolerant weeds increased by 50 percent last year – opinion differs over the root cause of the problem. Chemical manufacturers blame greedy farmers, who neglected best practice for the superweeds, whereas sustainable agriculture experts maintain that resistance is inevitable, and that by not following guidelines some farmers may only have exacerbated a latent problem with the chosen approach to weed management.  

Dr Marcia Ishii-Eiteman, a senior scientist at Pesticide Action Network, commented at the time of Professor Benbrook's work, "Rather than reducing the need for hazardous pesticides, herbicide-resistant seeds have driven a massive increase in herbicide use that has been linked to significant environmental and public health concerns. It's clear that genetically engineered, herbicide-resistant seeds are the growth engines of the pesticide industry's sales and marketing strategy. These seeds are part of a technology package explicitly designed to facilitate increased, indiscriminate herbicide use and pump up chemical sales."