Graham Brookes of PG Economics documented and analyzed the trends of weed control changes and herbicide tolerant (HT) crops in the USA from 1996 to 2012. The findings are published in GM Crops and Food journal.

According to the report, the use of HT technology resulted to net reduction in both the amount of herbicide used and associated environmental impact when compared to the use of conventional production methods. HT technology facilitated many farmers to switch from plough-based to no-tillage or conservation tillage production system and reap economic and environmental advantages. A broad range of, mostly selective herbicides has been replaced by one or 2 broad-spectrum herbicides (mostly glyphosate) used in conjunction with one or 2 other (complementary) herbicides. By mid-2000, herbicide application and the associated environmental load have increased on both HT and conventional crops. The main reason for such is the increasing incidence of weed species developing populations resistant to herbicides and increased awareness of the growers on the consequences of using limited number of herbicides for weed control. Thus, growers use other herbicides in combination with glyphosate even if weed resistance to glyphosate have not been found. This strategy is influenced by their desire to continue using no-tillage or conservation tillage production system.

Read more at http://www.tandfonline.com/doi/full/10.4161/21645698.2014.958930#.VKyI1yuUfE0.