Weed resistance development and management in herbicide-tolerant crops: experiences from the USA

Abstract

The evolution of weeds in USA agroecosystems predates herbicide tolerant (HT) crops by several decades. However, given the unprecedented adoption of genetically engineered (GE) HT crops, particularly in maize, cotton and soybean and the concomitant use of glyphosate, the evolution of glyphosate-resistant (GR) biotypes of agronomic important weeds now represents a significant threat to the sustainability of the GE HT trait and the herbicide. Notably, GR biotypes of horseweed (Conyza canadensis), common waterhemp (Amaranthus tuberculatus), Palmer pigweed (Amaranthus palmeri), giant ragweed (Ambrosia trifida) and johnsongrass (Sorghum halepense) have increased dramatically in frequency in conjunction with the adoption of crop production systems based on GE HT crops. Furthermore, other shifts in weed communities have been observed. It must be emphasized that the GE HT crops did not directly cause these weed shifts. The industry was responsible initially for these changes in weed communities given their initial positions that the glyphosate-resistant weed problems were unlikely to evolve and the recommendations to use glyphosate exclusively for weed management. However, decisions by growers to use glyphosate must be factored in as imparting selection pressure on the weed communities resulting in weed management problems, particularly when university recommendations strongly suggested not to use glyphosate in this manner. The key is now to provide growers with sufficient information to convince them to adopt integrated weed management programs and utilize best management practices. Given the presumed and real benefits of convenience and simplicity of the GE HT crop production systems; this will be a difficult task.

Sustainability and innovation in staple crop production in the US Midwest

“…GM crops have maintained or increased US pesticide use relative to equally advanced competitors. The pattern and quantities unique to the use of GM-glyphosate-tolerant crops has been responsible for the selection of glyphosate-tolerant weeds, with estimates of resistant weeds on International Journal of Agricultural Sustainability between 6 and 40 million hectares in the United States (Waltz 2010, Owen 2011, Benbrook 2012, Heap et al 2013. The use of Bt crops is associated with the emergence of Bt resistance and by novel mechanisms in insect pests (Lu et al 2010, Waltz 2010, Benbrook 2012, Zhang et al 2012.…”

Herbicide-tolerant Transgenic Soybean over 15 Years of Cultivation: Pesticide Use, Weed Resistance, and Some Economic Issues. The Case of the USA

“…It should be noted that not all HT varieties are transgenic [6]. Others exist through mutagenesis or conventional breeding methods, but, until recently, they generally raised both less interest because their efficiency was lower, and less controversy because they were not GMOs.…”

“…In the 1990s Monsanto considered there was almost no risk of the occurrence of GR weeds [6,60]. Thus advice for good weed management was most likely not provided at the beginning of the diffusion of HT varieties, and the weed scientists who did provide some were hardly listened to.…”

One-step, codominant detection of imidazolinone resistance mutations in weedy rice (Oryza sativa L.)

“…Weed population monitoring is part of an integrated strategy for herbicide resistance prevention and control [19]. The sustainability of herbicide-resistant crop production relies on a proactive management of herbicide resistance in weed populations [20]. This approach should involve the monitoring of WR populations for early detection of RWR to identify risky situations and take timely actions that prolong the life span of the Clearfield rice production system.…”