Environmental impact of herbicide regimes used with genetically modified herbicide-resistant maize

Abstract

With the potential advent of genetically modified herbicide-resistant (GMHR) crops in the European Union, changes in patterns of herbicide use are predicted. Broad-spectrum, non-selective herbicides used with GMHR crops are expected to substitute for a set of currently used herbicides, which might alter the agro-environmental footprint from crop production. To test this hypothesis, the environmental impact of various herbicide regimes currently used with non-GMHR maize in Belgium was calculated and compared with that of possible herbicide regimes applied in GMHR maize. Impacts on human health and the environment were calculated through the pesticide occupational and environmental risk (POCER) indicator. Results showed that the environmental impact of herbicide regimes solely relying on the active ingredients glyphosate (GLY) or glufosinate-ammonium (GLU) is lower than that of herbicide regimes applied in non-GMHR maize. Due to the lower potential of GLY and GLU to contaminate ground water and their lower acute toxicity to aquatic organisms, the POCER exceedence factor values for the environment were reduced approximately by a sixth when GLY or GLU is used alone. However, the environmental impact of novel herbicide regimes tested may be underestimated due to the assumption that active ingredients used with GMHR maize would be used alone. Data retrieved from literature suggest that weed control efficacy is increased and resistance development delayed when GLY or GLU is used together with other herbicides in the GMHR system. Due to the partial instead of complete replacement of currently used herbicide regimes, the beneficial environmental impact of novel herbicide regimes might sometimes be reduced or counterbalanced. Despite the high weed control efficacy provided by the biotechnology-based weed management strategy, neither indirect harmful effects on farmland biodiversity through losses in food resources and shelter, nor shifts in weed communities have been demonstrated in GMHR maize yet. However, with the increasing adoption rate of GMHR maize and their associated novel herbicide regimes, this situation is expected to change in the short-term.

Coexistence of genetically modified (GM) and non-GM crops in the European Union. A review

“…In the case of GM herbicide-resistant crops, the biotechnology-based weed management strategy is thought to replace a set of currently used herbicides by broad-spectrum, non-selective herbicides with better environmental profiles, and to reduce the amount of active ingredients applied and herbicide doses used (Nelson and Bullock, 2003;Brimner et al, 2005;Cerdeira and Duke, 2006;Graef et al, 2007;Kleter et al, 2007Kleter et al, , 2008Bonny, 2008;Devos et al, 2008b;Duke and Powles, 2008;Gardner and Nelson, 2008;Shipitalo et al, 2008). The adoption of GM herbicide-resistant crops and their associated management practices might (i) increase the flexibility in timing of weed management; (ii) simplify weed management; (iii) reduce management time; (iv) lower the risk for crop injury; (v) facilitate the adoption of no-till or reduced-till planting procedures; and (vi) generate less concern with carry-over damage to rotational crops (Marra and Piggott, 2006;Sanvido et al, 2007;Devos et al, 2008b;Duke and Powles, 2008;Gianessi, 2008). Where higher-than-average herbicide rates and numbers of active substances are needed for weed control, improved control of troublesome weeds combined with a reduction in overall herbicide-use rates and number of used active ingredients might translate into economic benefits for farmers.…”

Limits of Concern: suggestions for the operationalisation of a concept to determine the relevance of adverse effects in the ERA of GMOs

“…Changes in weed management decisions are difficult to assess during the pre-market ERA of GMOs as they involve a comparison with the weed management decisions in conventional crops that differ regionally and temporally throughout the EU. Current herbicide regimes in soybean or maize include the application of pre-emergence and/or post-emergence residual or foliar herbicides [77, 79, 113]. The number of post-emergence herbicide applications in conventional maize ranges from 0.4 to 2.3 depending on the country [114].…”

“…The predicted herbicide regimes for GMHT soybean or maize in the EU include two scenarios: the substituted post-emergence herbicide application (see, e.g. substitution scenario in [77, 79]) and the worst-case scenarios with different non-selective herbicide applications combined with residual herbicides [77, 79, 113]. …”

Scientific Opinion on application (EFSA-GMO-UK-2008-60) for placing on the market of genetically modified herbicide tolerant maize GA21 for food and feed uses, import, processing and cultivation under Regulation (EC) No 1829/2003 from Syngenta Seeds

“…Currently, the control of weeds in maize is mostly achieved by using preemergence soil acting residual herbicides and/or post-emergence selective herbicides in Europe. On the basis of environmental impact indices, a large number of authors have claimed that some of the herbicidal active substances used on GMHT crops (e.g., glyphosate) have reduced environmental impacts compared with those applied on their conventional counterparts (Nelson and Bullock, 2003;Peterson and Hulting, 2004;Brimner et al, 2005;Brookes and Barfoot, 2006;Leroux et al, 2006;Kleter et al, 2007;Bonny, 2008Bonny, , 2011Devos et al, 2008;Arregui et al, 2010;Mamy et al, 2010). In the current legislation governing the registration of plant protection products in Europe, the environmental risk assessment of pesticides includes an assessment of impacts on certain non-target organisms (such as fish, Daphnia, algae, birds, mammals, earthworms, bees and beneficial arthropods and non-target plants) and studies of residual activities in soil and water (cf., environmental fate) (Streloke, 2011).…”

“…Several strategies have been proposed for controlling weeds in GMHT maize depending upon the spectrum and density of weeds present at or just after sowing (reviewed by Beckie et al, 2006;Devos et al, 2008;Dewar, 2009Dewar, , 2010 54 .…”