25 Years of Glyphosate-Tolerant Crops: What We Have Learned and How to Face the New Challenges

Dear Colleagues,

The coupling of glyphosate-tolerant crops with glyphosate-based herbicides is the main weed management strategy in corn, soybean, cotton, and canola, in several countries worldwide (e.g., United States, Brazil, Argentina, Canada, India). The development of herbicide-tolerant crops was an outstanding scientific breakthrough, aiming initially at facilitating weed control and reducing herbicide use. Indeed, glyphosate is a non-selective, systemic, and non-residual herbicide. It can be used before sowing (burndown applications), during the growing season on tolerant crops or before harvest as a desiccant for non-tolerant crops. Initially, applying glyphosate-based herbicides replaced the need to apply other active ingredients in tolerant crops, with the other available active ingredients most often being more harmful than glyphosate (e.g., atrazine). 

However, twenty-five years after their introduction on the market new challenges have arisen, such as the development of glyphosate-resistant weeds, the occurrence of volunteer crop plants in glyphosate-tolerant planted crops, and an extraordinary increase in the sales volume for glyphosate-based herbicides with an increased detection of glyphosate and its by-product aminomethylphosphonic acid (AMPA) in waterways. A current strategy to cope with weed resistance is the development of crops with stacked genes for multiple herbicide tolerance. Unfortunately, this strategy requires the spraying of multiple active ingredients on field. Most of these are more toxic than glyphosate, which increases the environmental and human health risks. Therefore, it seems that the adoption of glyphosate-tolerant crops coupled with glyphosate-based applications does not offer a complete answer regarding weed management and sustainability. 

This Special Issue aims to foster a conversation about the agronomic and environmental challenges related to the adoption of glyphosate-tolerant crops and glyphosate-based herbicide applications, and about solutions proposed to help cope with some of these new challenges. Research areas may include (but are not limited to) the following:

• Glyphosate-resistant weeds;
• Mechanisms of resistance to glyphosate;
• Control of volunteer crop plants;
• Integrated weed management in glyphosate-tolerant crops;
• Environmental risk assessment;
• Herbicides and plant physiology;
• Analytical development for pesticide residue analysis. 

We are pleased to invite you to contribute to this Special Issue, where original research articles, reviews, opinion pieces and mini-reviews are welcome.

We look forward to receiving your contributions.

Dr. Élise Smedbol
Dr. Guilherme Braga Pereira Braz
Dr. Eloisa Dutra Caldas
Guest Editors

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• glyphosate resistant weeds
• volunteer crop plants
• integrated weed management
• EPSP synthase enzyme
• herbicide residues
• herbicide environmental fate
• plant physiology