10. Dr. Katherine Hauge-Madsen, KVL, Denmark, presented the benefits and potential environmental impacts of herbicide resistance crops (HRC). She noted that, among the GM crops being cultivated worldwide, about 83% of the area is planted with HRC including soybean, maize, cotton and canola. HRC offer new options for herbicide use to control weeds; helps reduce tillage, prevents soil erosion and preserves soil moisture for plant production. Effective farm management and improved efficiency were the main reasons for commercial success of HRC. However, she cautioned that short-term benefits could be jeopardized by some unwanted impacts in the longer run. They could occur at field level e.g. in weed control or on the environment. Within an ecosystem, non-target species could be affected by the widespread cultivation of HRC because of shifts in weed control and in the equilibrium of population dynamics between the weed species in the field, and insects, birds and small mammals that feed on them. At the field level, 'outcrossing' from HRC to a weedy species or to crops without the HR trait and/or spread of HRC seeds, combined with the effects of herbicide use, are the main processes that could lead to environmental problems. Outcrossing is a natural phenomenon and requires the successful dispersal of the gene through pollen, the presence of a wild cross-compatible out-crossing species in the vicinity and overlapping flowering periods of the two species. The issues related to high selection pressure on naturally occurring resistant biotypes of weeds was a cause of concern and the first glyphosate-resistant annual broadleaf weed Conyza canadensis has already been detected in glyphosate-resistant soybean systems. It was emphasised that the potential effects of outcrossing and selection for resistant weeds however, should be compared to the properties of currently used herbicides, which are often less environmentally benign than the herbicides used in HRC.
The expert summarised that HRC offered significant benefits. Countries/regions should establish a mechanism for approval of national/regional use of HRC and ensure long term benefits for farm management and the environment. The mechanism should be based, at least in part, on assessment of agricultural and environmental effects and should be carried out prior to the release of the HRC on a case-by-case basis. Good agriculture management practices should be encouraged, which could include record keeping at the farm level, crop rotation, maintenance of minimum temporal and spatial distance between HRC and non-resistant varieties of the same crop, regular monitoring of weed flora and its shift in order to detect the species which are evolving resistance, and quick management decisions following detection of resistant volunteers.
11. During the discussion, the participants agreed that the current range of HRC has assisted in increasing crop production by providing an effective and convenient weed control strategy and to date, no major negative environmental effects have been reported. Experts cited several ongoing large-scale studies being conducted in Canada and UK, which were assessing the impact of gene flow in canola and other crops. The experts were of the opinion that the exact cause for the emergence of the resistant weed Conyza canadensis in glyphosate-resistant soybean systems needed to be ascertained. The key points of the discussion were as follows:
