1) Roundup Ready crops increased the use of herbicides and triggered the development of glyphosate resistant crops

• In the lead biotech countries, glyphosate use rose dramatically since the introduction of RR crops and also total herbicide use rose in those countries. ^{1, 2, 3, 4, 5, 6, 7}
• Contrary in countries that do not cultivate RR crops, such as France, Germany and Switzerland a downward trend of pesticide use was observed. ⁸  

• One of the main reasons for the increase in herbicide use in RR crop adopting countries is the widespread emergence of glyphosate resistant weeds, also referred to as ‘superweeds’, although Monsanto scientists originally rated such a development as ‘highly unlikely’.  ^{1, 9, 10, 11, 12, 13, 14}
  

• Superweeds not only force farmers to increase their herbicide application rates and apply additional herbicides but also to go back to the costly, time- and labour-intensive weed control measures, thereby increasing overall costs for weed management and eliminating the main advantage of RR crops.  ^{1, 11, 15, 16, 17, 18, 19, 20}
• Today there are 32 known weed species that have evolved resistance to glyphosate.  ⁹
• In 2012, one-third to fifty percent of the land planted to RR crops in the U.S. was infested with at least one glyphosate resistant weed and the trend is rising  ^{21, 22}
• Glyphosate resistant weeds can lead to complete crop failure.  ¹⁵

2) Increasing costs for seeds

• In the U.S., overall seed prices rose rapidly since the introduction of GM crops  ²³ and this increase in seed price is not compensated with equally rising prices for crops.  ^{21, 24}
• RR seeds are more expensive than conventional seeds  ^{1, 21, 25}
• Biotech companies have implemented a ‘technology’ or ‘trait fee’, that is charged in addition to basic seed costs. This trait fee is also rising. ²⁶
• Non-GM seed prices are said to be artificially elevated to encourage farmers to continue buying GM crops.  ²⁷
• Strict intellectual property rights prevent farmers from their customary habit of seed saving. Instead they have to purchase new seed every year from the biotech companies, which additionally results in higher costs for seed.  ²⁸

3) No clear yield increase

• Herbicide tolerant crops are designed to kill weeds in order to approach the highest possible yield that the genetics of the crop allow. They do not have an increase yield potential compared to conventional varieties. Their value depends on pest pressure.  ^{29, 20, 31, 32, 33}
• One of the most extensive literature reviews on yield contribution of GM corn, using 163,941 experimental trials conducted between 1997 and 2009 in the most important maize producing U.S. states, found no yield benefits for single herbicide tolerant traits.  ³²
• Field studies conducted in the U.S. state Wisconsin from 1990-2010, show a lower average yield for glyphosate resistant maize compared to conventional maize.  ³⁴
• In North America, yield benefits do neither in absolute numbers nor in their yield growth per year exceed those of Western Europe where as of today no RR crops are cultivated. This is also true for Spain, the only European country that grows herbicide resistant crops on a large scale.  ^{8, 35, 36}
• The recorded increase of crop yields over the last 15 years is more likely to result from traditional breeding than from herbicide resistant crops and due to improvements of agricultural practices. ^{29, 30, 37, 38}
• Environmental parameters such as early season drought or reduced solar radiation at critical growth stages have a much bigger influence on yield than the type of hybrids used.  ³³
• There is concern that the widespread use of glyphosate in RR cropping systems may impact crop growth, productivity and ultimately grain yield in that it decreases macro and micro nutrient uptake, translocation and accumulation, photosynthetic parameters and increases susceptability to certain fungal diseases such as Fusarium.  ^{39, 40, 41, 42, 43, 44, 45, 46, 47, 48} Lower content of essential nutrients and altered seed composition can also have implications for animal and human health.

4) Adverse impact on farmland biodiversity

• Results from the Farm Scale Evaluations (FSE) of herbicide tolerant crops in the UK showed that management practices in herbicide resistant oilseed rape and beet compared to conventional oilseed rape and beet decrease overall weeds and weed seeds and can on the long term deplete seed stores beyond recovery. This was also shown to affect insects such as butterflies and bees and farmland birds that depend on weeds and weed seeds. ^{49, 50, 51, 52}
• The iconic Monarch butterfly that travels south to Mexico in fall to overwinter and back to North America in spring, producing multiple generations of new butterflies, is endangered. Named reasons for its vast decline of 90% in only 20 years are loss of overwintering sites due to illegal logging in Mexico, severe weather conditions and most importantly the loss of milkweed plants, the sole food of the larvae, associated with increased glyphosate use in RR crop fields.  ^{53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63}
• Sublethal effects of glyphosate on honeybees, key pollinators and extremely important for our food security, have been shown. ^{64, 65, 66} This demonstrates that only looking at lethal effects in environmental risk assessments is insufficient.
• Glyphosate-based formulations have been shown to be toxic to many aquatic organisms such as algae, aquatic plants, protozoa, crustaceans, molluscs, amphibians and fish, each playing an important role for the functioning of an aquatic ecosystem. ^{67, 68, 69, 70, 71, 72, 73, 74, 75, 76}
• Adjuvants, whose function within herbicide formulations is to enhance the chemical and physical efficacy of the active ingredient, are more toxic to aquatic organisms than glyphosate alone. This shows that testing glyphosate alone in environmental risk assessments is insufficient. ^{77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90}

5) Adverse impact on human health

• In vitro, clinical and epidemiological studies have shown that glyphosate-based formulations possibly pose serious health hazards, including cell death, disruption of hormonal systems, DNA damage, cell cycle dysfunction and cancer, malformations and birth defects amongst others. ^{91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108}
• In 2015 the World Health Organisation’s (WHO) cancer agency, the International Agency for Research on Cancer (IARC), classified glyphosate as “probably carcinogenic to humans”, citing different studies that reported increased risk for non-Hodgkin lymphoma and other types of cancer such as skin tumours or the rare tumour renal tubule carcinoma ^{109, 110}

References

(1)    Benbrook, C. M. (2012). Impacts of genetically engineered crops on pesticide use in the U.S. -- the first sixteen years. Environmental Sciences Europe, 24(1), 24. doi:10.1186/2190-4715-24-24. For the numbers of herbicides applied to conventional and HR crop acres see Additional file 1: Tables 8, 9 & 10.
(2)    Carneiro, F. F., Rigotto, R. M., Da Silva Augusto, L. G., Friedrich, K., Campos Búrigo, A. (2015). Dossiê ABRASCO: um alerta sobre os impactos dos agrotóxicos na saúde . Rio de Janeiro: EPSJV; São Paulo: Expressão Popular, 2015. http://aspta.org.br/wp-content/uploads/2015/05/DossieAbrasco_2015_web.pdf
(3)    CASAFE (2014). Estudio de Mercado de Fitosanitarios 2013.http://www.casafe.org.ar/pdf/EstudioFitosanitarios.pdf

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