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Traits in Agriculture » Herbicide Tolerance

Title: GM Herbicide-Resistant Crops Have Adverse Impacts on Biodiversity
Publication date: March 14, 2017
Posting date: March 14, 2017

THIRD WORLD NETWORK BIOSAFETY INFORMATION SERVICE

 

Dear Friends and Colleagues

GM Herbicide-Resistant Crops Have Adverse Impacts on Biodiversity

Farmland biodiversity is an important characteristic when assessing the sustainability of agricultural practices and is of major international concern as shown by the Convention on Biodiversity (CBD) and the various decisions since then. A team of researchers have condensed and updated (Item 1) a comprehensive technical report on the agronomic and environmental aspects of the cultivation of genetically modified (GM) herbicide-resistant (HR) plants which was previously published by the German Federal Agency for Nature Conservation (BfN), the Austrian Environment Agency (EAA), and the Swiss Federal Office for the Environment (FOEN). A detailed supplement paper is also now available (Item 2). Key points of both papers follow, and we reproduce their respective Abstract and Conclusions below.

Scientific data indicates that agricultural intensification and pesticide use are among the main drivers of biodiversity loss. Given the actual trends in cultivation from the 1990s, the GM HR crop system has not increased yields significantly nor reduced herbicide use. Glyphosate-based herbicides have been shown to be toxic to a range of organisms and to adversely affect soil and intestinal microflora and plant resistance to disease while glufosinate exhibits reproductive toxicity to mammals and will be phased out in the EU in 2017.

The adoption of GM HR crops has reduced crop rotation and favoured weed management that is solely based on and increased the use of herbicides. Continuous GM HR cropping and the intensive use of glyphosate over the last 20 years has led to the appearance of at least 34 glyphosate-resistant weed species infesting millions of farmland hectares worldwide. Experience with such crop systems over several years shows that broad-spectrum herbicide application further decreases diversity and the abundance of wild plants, in particular of broad-leaf plants, and impacts arthropod fauna and other farmland animals.

Taken together, adverse impacts of GM HR crops on biodiversity, when widely adopted, are very hard to avoid. From a nature protection perspective, such crops seem to be no option for a sustainable agriculture focusing also on protecting biodiversity. To avoid further adverse impacts on biodiversity, agriculture needs to focus on practices that are more environmentally friendly, including an overall reduction in pesticide use.

With best wishes,

Third World Network
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Email: twn@twnetwork.org
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Item 1

HERBICIDE RESISTANCE AND BIODIVERSITY: AGRONOMIC AND ENVIRONMENTAL ASPECTS OF GENETICALLY MODIFIED HERBICIDE-RESISTANT PLANTS

Schütte, G., Eckerstorfer, M., Rastelli, V., Reichenbecher, W., Restrepo-Vassalli, S., Ruohonen-Lehto, M., ... & Mertens, M.

Environmental Sciences Europe, 29(1), 5. 2017.

DOI: 10.1186/s12302-016-0100-y
http://enveurope.springeropen.com/articles/10.1186/s12302-016-0100-y

Abstract


Farmland biodiversity is an important characteristic when assessing sustainability of agricultural practices and is of major international concern. Scientific data indicate that agricultural intensification and pesticide use are among the main drivers of biodiversity loss. The analysed data and experiences do not support statements that herbicide-resistant crops provide consistently better yields than conventional crops or reduce herbicide amounts. They rather show that the adoption of herbicide-resistant crops impacts agronomy, agricultural practice, and weed management and contributes to biodiversity loss in several ways: (i) many studies show that glyphosate-based herbicides, which were commonly regarded as less harmful, are toxic to a range of aquatic organisms and adversely affect the soil and intestinal microflora and plant disease resistance; the increased use of 2,4-D or dicamba, linked to new herbicide-resistant crops, causes special concerns. (ii) The adoption of herbicide-resistant crops has reduced crop rotation and favoured weed management that is solely based on the use of herbicides. (iii) Continuous herbicide resistance cropping and the intensive use of glyphosate over the last 20 years have led to the appearance of at least 34 glyphosate-resistant weed species worldwide. Although recommended for many years, farmers did not counter resistance development in weeds by integrated weed management, but continued to rely on herbicides as sole measure. Despite occurrence of widespread resistance in weeds to other herbicides, industry rather develops transgenic crops with additional herbicide resistance genes. (iv) Agricultural management based on broad-spectrum herbicides as in herbicide-resistant crops further decreases diversity and abundance of wild plants and impacts arthropod fauna and other farmland animals. Taken together, adverse impacts of herbicide-resistant crops on biodiversity, when widely adopted, should be expected and are indeed very hard to avoid. For that reason, and in order to comply with international agreements to protect and enhance biodiversity, agriculture needs to focus on practices that are more environmentally friendly, including an overall reduction in pesticide use. (Pesticides are used for agricultural as well non-agricultural purposes. Most commonly they are used as plant protection products and regarded as a synonym for it and so also in this text.)


Item 2

SUPPLEMENT — HERBICIDE RESISTANCE AND BIODIVERSITY: AGRONOMIC AND ENVIRONMENTAL ASPECTS OF GENETICALLY MODIFIED HERBICIDE-RESISTANT PLANTS 

Conclusions

The need to protect biodiversity and stop its loss is an internationally agreed goal. Scientific data give evidence that intensive high-input farming is one of the main drivers of ongoing biodiversity loss in agricultural landscapes. Diversity and abundance of the weed flora provide relevant indicators for farmland biodiversity.

HR crops, introduced in the 1990’s, facilitate weed control for farmers and make chemical weed management more flexible. Yield increase is not the main reason for adoption of HR crops, as there has been little, if any, contribution of HR crops to increase yield. HR crops are adopted primarily due to the expected lower costs, less labour and fuel consumption.

HR cropping is associated with the use of broad-spectrum herbicides. While glufosinate, due to its reproductive toxicity, is expected to be phased out in the EU in 2017, glyphosate is presently evaluated for renewed approval in the EU. It is today the most widely used herbicide in the world. In general, eco-toxicity of glyphosate has been considered to be low, compared to some other herbicides, but data collected within the last years indicate that glyphosate-based herbicides can be toxic not only to plants, but also to other life forms, in particular to aquatic species and to amphibians. Adverse effects on the soil microflora and fauna and on plant disease resistance have been reported.

Lower herbicide use may have been a benefit in the first years of HR cropping in the US, but the trend turned around 2000 and since then, herbicide use, in particular of glyphosate, increased almost steadily. The trends are similar in other countries with HR crop cultivation, such as Argentina. Should HR crops be authorized for cultivation in the EU, a significant increase in herbicide use can be expected.

In regions where HR crops are widely adopted, mechanical weed control decreased and less crop rotation and crop diversification takes place, whereas reduced till or no-till practices expanded. There is a clear trend towards monoculture of HR crops, which enhances disease and pest pressure.

Increased dependence on herbicides for weed control leads to a shift in weed species composition. Although glyphosate was not considered to be a high-risk herbicide with regard to resistance development, its intensive use has led to the appearance of at least 34 glyphosate-resistant weed species (17 dicots and 17 monocots) comprising more than 240 populations and infesting millions of hectares. These biotypes exhibit a great diversity of molecular and genetic resistance mechanisms and some of them are cross-resistant to other herbicides. Recently, two weed species resistant to glufosinate have been described as well.

To combat resistance development in weeds, weed scientists recommend that farmers should use a variety of weed management methods and not rely solely on herbicides. But fus and widespread glyphosate-resistant cropping has became common in the Americas and farmers often simply resort to higher herbicide doses and other herbicide modes of action. Increasingly, companies develop and commercialize transgenic crops with stacked HR traits, among them resistance to herbicides such as synthetic auxins or ALS-inhibitors. However, a number of hard to control weeds is already resistant to these herbicides.

In addition to herbicide-resistant weeds, control problems can also arise due to volunteers of HR crops. Oilseed rape is a particularly likely volunteer, as its small long-lived seeds are easily spilled in and outside fields and along transport routes. Volunteers and feral plants, resistant to glyphosate and glufosinate have been detected in fields and areas where HR crops have not been planted previously.

Oilseed rape plants with multiple HR genes not commercially sold provide evidence of novel transgene combinations in the wild. Thus, the HR trait can spread both spatially and temporally. If outcrossing of HR crops into the same or related species occurs, more HR plants might show up. Such transfer of HR genes to wild relatives should particularly be taken into account and avoided in centres of crop origin and regions where sexually compatible and weedy hybrids occur.

The Farm Scale Evaluations have provided ample evidence that in HR systems, compared to conventional farming, weeds are removed more efficiently, leading to a further reduction of flora and fauna diversity and abundance in farmland. A prominent example in this respect may be the significant reduction in monarch butterfly populations in the US which has been linked to the widespread cultivation of HR crops in the Midwest leading to a massive loss of milkweed plants, on which monarch larvae feed.

As agricultural intensification and pesticide use are among the main drivers of biodiversity loss, agreement is required on farming practices that are more environmentally friendly and less dependent on pesticides. But the lessons learnt in HR crop adopting countries indicate that herbicide use is increasing with this technology. Therefore, it is highly questionable whether present HR systems comply with measures to stop the loss of biodiversity on farmland or can be managed in a sustainable way. From a nature protection perspective, HR crops seem to be no option for a sustainable agriculture focusing also on protecting biodiversity. To avoid further adverse impacts on biodiversity, a different approach to agriculture is clearly necessary.


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