Influence of herbicide‐resistant canola on the environmental impact of weed management

Abstract

The growth of herbicide-resistant canola varieties increased from 10% of the canola area in Canada in 1996, when the technology was first introduced, to 80% in 2000. From 1995 to 2000, the amount of herbicide active ingredient applied per hectare of canola declined by 42.8% and the Environmental Impact (EI) per hectare, calculated using the Environmental Impact Quotient for individual herbicides and the amounts of active ingredients applied, declined 36.8%. The amount of herbicide active ingredient per hectare applied to conventional canola was consistently higher than that applied to herbicide-resistant canola each year between 1996 and 2000. Similarly, the EI of herbicide use per hectare in conventional canola was higher than that of herbicide-resistant canola during the same time period. Since 1996, herbicide use has shifted from broadcast applications of soil-active herbicides to post-emergence applications of herbicides with broad-spectrum foliar activity. The decline in herbicide use and EI since the introduction of herbicide-resistant varieties was due to increased use of chemicals with lower application rates, a reduced number of applications and a decreased need for herbicide combinations.

Ecological compatibility of GM crops and biological control

“…But the degree to which herbicide usage is altered by the adoption of herbicide-tolerant varieties is largely dependent on crop-specific production practices. For example, overall herbicide use in canola is reduced in herbicidetolerant fields versus conventional fields (Brimner et al, 2005).…”

Weed control, environmental impact and profitability of reduced rates of imazethapyr in combination with dimethenamid in dry beans

“…The EI was designed to provide growers and weed management practitioners with a single number that indicates the magnitude of relative risk. Despite criticism mainly due to simplicity (Dushoff et al 1994), EI has been used effectively by several researchers to compare environmental risk of different pesticides and/or production systems (Fernandez-Cornejo 1998;Edwards-Jones and Howells 2001;Ziegler et al 2002;Bues et al 2003, Lan et al 2003Brimner et al 2005). The EI can be used as a decision tool, along with herbicide efficacy, crop safety, and profit margins to identify the most advantageous weed management strategy in dry beans.…”

Ecological Impacts of Genetically Modified Crops: Ten Years of Field Research and Commercial Cultivation

“…Studies can be found to support this view [151,152], but there appear to be more studies that support a small but statistically significant reduction in herbicide use [140,[153][154][155]. Because the reduction varies between crops and regions, it is difficult to draw a general conclusion.…”

“…Because the reduction varies between crops and regions, it is difficult to draw a general conclusion. The adoption of GMHT varieties of oilseed rape in Canada, for example, has been associated with a reduction in the amount of herbicide used per hectare as well as a decline in the potential environmental impact of chemical weed management [153]. The average soybean herbicide application rates in the U.S., in contrast, have slightly increased by 3% since the introduction of GMHT soybean (in terms of active ingredients per acreage) [140,155].…”

“…GMHT crop varieties allow the use of a single broad-spectrum herbicide that has a wider spectrum of activity and that may reduce the need for herbicide combinations or chemicals that require multiple applications [153,155,156]. The herbicides used in GMHT crops (glyphosate or glufosinate) are foliar-applied, postemergence herbicides, which usually allow using herbicides in a more targeted manner.…”