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Can We Expect New Herbicides with Novel Modes of Action in the Foreseeable Future?

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The need for new products with novel mechanisms of action is the case for all crop protection chemicals particularly so for herbicides, where there has been no major herbicide with a novel mode of action commercialised in the last two decades. The reasons for this are a result of three overall factors, which are largely economic (Duke, 2012).

Firstly, the major economic influence has been adoption of herbicide tolerant (HT) GM crops, notably maize and soybean, two crops which previously had been priority targets for new selective herbicide discovery within the agrochemical industry. The introduction of glyphosate tolerance in these crops introduced relatively low cost and effective weed control, albeit part of the cost for the herbicide was switched to a technology fee for the seed. The expiration of the patent for glyphosate also reduced on the cost of weed control with this herbicide as it became generic. Evidence for the loss of attractiveness for new herbicide discovery by the industry is seen by the significant decreases in new herbicide patents following the introduction of HT crops in the mid-1990s (Gerwick, 2010, Duke, 2012).

The second factor is the consolidation of the companies involved in crop protection chemical discovery. During the heyday of new herbicide discovery in the 1980s, when the majority of today’s herbicides were discovered there were over 20 separate agrochemical companies. Following a series of takeovers and mergers there were only the ‘Big Six’ multinational R&D-based companies remaining by the turn of the century (Copping, 2003). Herbicide discovery, as for insecticides and fungicides is based on empirical screening of diverse molecules. This coupled to different philosophical approaches from those engaged in new discovery in the 1980s, lead to the vast majority of herbicides that we have available for weed control today. Consolidation of companies conducting research since then, reduced the numbers of scientists involved and their approaches to new molecule discovery and as a result output of new molecules declined as seen by a significant reduction of new patents in the last decade (Ruegg et al., 2007; Gerwick, 2010; Duke, 2012).

A third factor is the cost of bringing a new crop protection molecule into the market, also a reason behind the industry consolidation. Development costs to bring a new molecule have increased. By 1995, costs were estimated at $250 million approximately 3 times that of the decade earlier (Ruegg et al., 2007). A breakdown of these costs shows all 4 major components: synthesis & screening; formulation, product analysis & process development; field trials & official testing; and regulatory studies (toxicology, eco-toxicology, environmental impact & metabolism) have all increased, those for the latter have increased more rapidly with 40% of the total costs in 1990–1995 were for regulation, whilst being 20–25% of the costs a decade earlier.

This explains how we have the downturn in new herbicides and I would now like to focus on how and when we can expect any new herbicides with novel modes of action. There have been several reviews in recent years highlighting the need for new herbicides with novel modes of action to meet resistance and legislative challenges and how this can been achieved (Cole et al., 2000; Duke, 2012; Kraehmer, 2012)

This article builds on these, introducing personal experience over the last 40 years in herbicide R&D by providing some further historical perspective on herbicide mode of action discovery, on the status of existing herbicide targets and discusses the prospects and challenges to find them.
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Keywords: HERBICIDE MODE OF ACTION; NEW HERBICIDE DISCOVERY PROCESSES

Document Type: Research Article

Publication date: 01 February 2016

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