NOTE: Problems are already emerging with Monsanto's new generation of Roundup Ready soybeans, RR2 Yield. It seems they are turning yellow in the field. The study below found that the reason for this is that glyphosate (Roundup) herbicide interferes with photosynthesis (the process by which plants use energy from sunlight to produce sugars).

That's on top of all the other problems glyphosate causes to plant and soil health--see breakdown of studies at
http://www.gmwatch.eu/images/pdf/gmsoy_sust_respons_full_eng_v12.pdf

Other studies have found that RR2 yields are disappointing and not living up to Monsanto's claims:
http://www.reuters.com/article/idUSN2515475920100625
---
---
Glyphosate affects photosynthesis in first and second generation of glyphosate-resistant soybeans
Zobiole, L.H.S., Kremer, R.J., de Oliveira, R.S., Constantin, J.
2010
Plant Soil 336, 251”šÄì265
http://www.springerlink.com/content/57115358w146h1r1/

Abstract

The crop area planted to conventional soybeans has decreased annually while that planted to glyphosate-resistant (RR) soybean has drastically increased mainly due to the wide adoption of glyphosate in current weed management systems. With the extensive use of glyphosate, many farmers have noted visual plant injury in RR soybean varieties after glyphosate application. A new generation designated as "second generation RR2" has been recently developed and these RR2 cultivars already are commercially available for farmers and promoted as higher yielding relative to the previous RR cultivars. However, little information is currently available about the performance of RR2 soybean beyond commercial and farmer testimonial data. Thus, an evaluation of different glyphosate rates applied in different growth stages of the first and second generation of RR soybeans, revealed a significant decrease in photosynthesis. In general, increased glyphosate rate and late applications (V6) pronounced decrease photosynthetic parameters and consequently decreased in leaf area and shoot biomass production. In contrast, low rate and early applications were less damage for the RR soybean plants, suggesting that with early applications (V2), plants probably have more time to recover from glyphosate or its metabolites effects regarding late applications.

Conclusion

Glyphosate caused undesirable effects on photosynthesis and biomass production in both first and second generation RR soybean. Results suggest that management strategies are needed to minimize these effects in the field, which could include using lower glyphosate rates as possible and early applications, with consideration of weed populations and the critical period of weed control, to assure optimum crop growth.