Herbicide discovery in light of rapidly spreading resistance and ever-increasing regulatory hurdles.

According to the United Nations, the global population is expected to grow to almost 10 billion people in 2050. This means that the demand for food, feed and fiber will double while at the same time, agriculture is being challenged by a scarcity of water, global warming, less land available for farming, protection of natural habitats, a demand for biodiversity on farms and other factors. In addition, crop protection products are under pressure from rapidly spreading resistance and increasing regulatory requirements. Many regulatory bodies are also moving away from a risk assessment approach to a more hazard-based approach to grant registrations. Nevertheless, chemical crop protection compounds remain attractive and necessary to combat pests, particularly weeds. Industry has increased its efforts to find new molecules that are highly biologically effective on target species, including resistant populations, but safe for non-target organisms. To manage resistance in the future, a diverse toolbox is needed that includes herbicides with a variety of different chemistries and modes of action, combined with non-chemical measures in integrated systems. However, discovering a herbicide and getting it registered and to the market is an extremely complex endeavor full of risk, much of it incalculable. © 2017 Society of Chemical Industry.

Herbicide resistance-what have we learned from other disciplines?

Herbicide resistance is a growing threat to agriculture and has parallels to resistances to fungicides and insecticides. However, there are many reasons to treat the resistance to herbicides differently. To highlight these similarities and differences, three pests, a weed, an insect, and a disease that have shown the ability to rapidly develop resistance to a variety of products and product classes were used as illustrations. The situation in herbicide resistance is approaching a point already experienced by the other pest control disciplines, and thus, it is worthwhile to revisit their experiences.

Characterization of glyphosate resistance in Amaranthus tuberculatus populations.

The evolution of glyphosate-resistant weeds has recently increased dramatically. Six suspected glyphosate-resistant Amaranthus tuberculatus populations were studied to confirm resistance and determine the resistance mechanism. Resistance was confirmed in greenhouse for all six populations with glyphosate resistance factors (R/S) between 5.2 and 7.5. No difference in glyphosate absorption or translocation was observed between resistant and susceptible individuals. No mutation at amino acid positions G101, T102, or P106 was detected in the EPSPS gene coding sequence, the target enzyme of glyphosate. Analysis of EPSPS gene copy number revealed that all glyphosate-resistant populations possessed increased EPSPS gene copy number, and this correlated with increased expression at both RNA and protein levels. EPSPS Vmax and Kcat values were more than doubled in resistant plants, indicating higher levels of catalytically active expressed EPSPS protein. EPSPS gene amplification is the main mechanism contributing to glyphosate resistance in the A. tuberculatus populations analyzed.

Improvement in day zero recoveries in field soil dissipation studies using larger diameter soil samples.

Obtaining acceptable recovery of the applied test substance at zero time in field soil dissipation studies has been a subject of considerable interest among scientists conducting regulatory field studies. In particular, achieving recoveries of ≥90% in soil samples collected immediately after applications in most studies has been elusive. This study investigated a modified soil sampling method, which could be used not only on day zero but for the entire study duration, to see if the recoveries in soil samples, especially in the early stages, can be improved. The modified sampling system has demonstrated that recoveries averaging 90% are possible and can be routinely obtained on day zero. Description of this modified sampling procedure and statistical analysis of the data collected for day zero samples are discussed.