Suitability of transgenic glyphosate-resistant soybeans to green cloverworm (Lepidoptera: Noctuidae)

Weeds and ground-dwelling predators' response to two different weed management systems in glyphosate-tolerant cotton: A farm-scale study

The use of glyphosate, as a post-emergence broad-spectrum herbicide in genetically modified glyphosate-tolerant (GT) cotton, supposes a big change in weed management programs with respect to a conventional regime. Thus, alterations in arable flora and arthropod fauna must be considered when evaluating their potential impacts. A 3-year farm-scale study was conducted in a 2-ha GT cotton crop, in southern Spain, to compare the effects of conventional and glyphosate herbicide regimes on weed abundance and diversity and their consequences for ground-dwelling predators. Surveys reveal that weed density was relatively low within all treatments with a few dominant species, with significantly higher weed densities and modifications of the floristic composition in glyphosate-treated plots that led to an increase in the abundance of Portulaca oleracea and to a reduction in plant diversity. The activity-density of the main predatory arthropod taxa (spiders, ground beetles, rove beetles and earwigs) varied among years, but no significant differences were obtained between conventional and glyphosate herbicide regimes. However, significant differences between treatments were obtained for ground beetles species richness and diversity, being higher under the glyphosate herbicide regime, and a positive correlation with weed density could be established for both parameters. The implications of these findings to weed control in GT cotton are discussed.

Coca and poppy eradication in Colombia: environmental and human health assessment of aerially applied glyphosate

The production of coca and poppy as well as the processing and production of cocaine and heroin involve significant environmental impacts. Both coca and poppy are grown intensively in a process that involves the clearing of land in remote areas, the planting of the crop, and protection against pests such as weeds, insects, and pathogens. The aerial spray program to control coca and poppy production in Colombia with the herbicide glyphosate is conducted with modern state-of-the-art aircraft and spray equipment. As a result of the use of best available spray and navigation technology, the likelihood of accidental off-target spraying is small and is estimated to be less than 1% of the total area sprayed. Estimated exposures in humans resulting from direct overspray, contact with treated foliage after reentry to fields, inhalation, diet, and drinking water were small and infrequent. Analyses of surface waters in five watersheds showed that, on most occasions, glyphosate was not present at measurable concentrations; only two samples had residues just above the method detection limit of 25 microg/L. Concentrations of glyphosate in air were predicted to be very small because of negligible volatility. Glyphosate in soils that are directly sprayed will be tightly bound and biologically unavailable and have no residual activity. Concentrations of glyphosate plus Cosmo-Flux will be relatively large in shallow surface waters that are directly oversprayed (maximum instantaneous concentration of 1,229microgAE/L in water 30cm deep); however, no information was available on the number of fields in close proximity to surface waters, and thus it was not possible to estimate the likelihood of such contamination. The formulation used in Colombia, a mixture of glyphosate and Cosmo-Flux, has low toxicity to mammals by all routes of exposure, although some temporary eye irritation may occur. Published epidemiological studies have not suggested a strong or consistent linkage between glyphosate use and specific human health outcomes. An epidemiology study conducted in Colombia did not show any association between time to pregnancy in humans and the use of glyphosate in eradication spraying. The mixture of glyphosate and Cosmo-Flux was not toxic to honeybees. The mixture was, however, more toxic to the alga Selenastrum, the cladoceran Daphnia magna, fathead minnow, and rainbow trout than formulated glyphosate (Roundup) alone. Studies on the use of glyphosate in agriculture and forestry have shown that direct effects on nontarget organisms other than plants are unlikely. Indirect effects on terrestrial arthropods and other wildlife may be the result of habitat alteration and environmental change brought about by the removal of plants by glyphosate. Because of the lack of residual activity, recovery of glyphosate-treated areas in Colombia is expected to be rapid because of good plant growth conditions. However, return to the conditions of tropical old-growth forest that existed before clear-cutting and burning may take hundreds of years, not from the use of glyphosate but because of the clear-cutting and burning, which are the primary cause of effects in the environment. The risk assessment concluded that glyphosate and Cosmo-Flux did not present a significant risk to human health. In the entire cycle of coca and poppy production and eradication, human health risks associated with physical injury during clear-cutting and burning and the use of pesticides for protection of the illicit crops were judged to be considerably more important than those from exposure to glyphosate. For the environment, direct risks from the use of glyphosate and Cosmo-Flux to terrestrial mammals and birds were judged to be negligible. Moderate risks could occur in aquatic organisms in shallow surface waters that are oversprayed during the eradication program. However, the frequency of occurrence and extent to which this happens are unknown as data on the proximity of surface waters to coca fields were not available. Considering the effects of the entire cycle of coca and poppy production and eradication, clear-cutting and burning and displacement of the natural flora and fauna were identified as the greatest environmental risks and are considerably more important than those from the use of glyphosate for the control of coca and poppy.

The current status and environmental impacts of glyphosate-resistant crops: a review

Glyphosate [N-(phosphonomethyl) glycine]-resistant crops (GRCs), canola (Brassica napus L.), cotton (Gossypium hirsutum L.), maize (Zea mays L.), and soybean [Glycine max (L.) Merr.] have been commercialized and grown extensively in the Western Hemisphere and, to a lesser extent, elsewhere. Glyphosate-resistant cotton and soybean have become dominant in those countries where their planting is permitted. Effects of glyphosate on contamination of soil, water, and air are minimal, compared to some of the herbicides that they replace. No risks have been found with food or feed safety or nutritional value in products from currently available GRCs. Glyphosate-resistant crops have promoted the adoption of reduced- or no-tillage agriculture in the USA and Argentina, providing a substantial environmental benefit. Weed species in GRC fields have shifted to those that can more successfully withstand glyphosate and to those that avoid the time of its application. Three weed species have evolved resistance to glyphosate in GRCs. Glyphosate-resistant crops have greater potential to become problems as volunteer crops than do conventional crops. Glyphosate resistance transgenes have been found in fields of canola that are supposed to be non-transgenic. Under some circumstances, the largest risk of GRCs may be transgene flow (introgression) from GRCs to related species that might become problems in natural ecosystems. Glyphosate resistance transgenes themselves are highly unlikely to be a risk in wild plant populations, but when linked to transgenes that may impart fitness benefits outside of agriculture (e.g., insect resistance), natural ecosystems could be affected. The development and use of failsafe introgression barriers in crops with such linked genes is needed.

Technical performance of some commercial glyphosate-resistant crops

Glyphosate-resistant (GR) crops have been sold commercially in the USA since 1996. The use of glyphosate alone or with conventional pre- and post-emergence herbicides with different modes of action gives growers many options for affordable, safe, easy, effective wide-spectrum weed control. Despite the overwhelming popularity of this technology, technical issues have surfaced from time to time as US growers adopt these crops for use on their farms. The types of concern raised by growers vary from year to year depending on the crop and the environment, but include perceptions of increased sensitivity to diseases, increased fruit abortion, reduced pollination efficiency, increased sensitivity to environmental stress, and differences in yield and agronomic characteristics between transgenic and sister conventional varieties. Although several glyphosate-resistant crops are commercially available, maize, soybean and cotton constitute the largest cultivated acreage and have likewise been associated with the highest number of technical concerns. Because glyphosate is rapidly translocated to and accumulates in metabolic sink tissues, reproductive tissues and roots are particularly vulnerable. Increased sensitivity to glyphosate in reproductive tissues has been documented in both glyphosate-resistant cotton and maize, and results in reduced pollen production and viability, or increased fruit abortion. Glyphosate treatments have the potential to affect relationships between the GR crop, plant pathogens, plant pests and symbiotic micro-organisms, although management practices can also have a large impact. Despite these potential technical concerns, this technology remains popular, and is a highly useful tool for weed control in modern crop production.