Why have no new herbicide modes of action appeared in recent years?

Abstract

Herbicides with new modes of action are badly needed to manage the evolution of resistance of weeds to existing herbicides. Yet no major new mode of action has been introduced to the market place for about 20 years. There are probably several reasons for this. New potential products may have remained dormant owing to concerns that glyphosate-resistant (GR) crops have reduced the market for a new herbicide. The capture of a large fraction of the herbicide market by glyphosate with GR crops led to significantly diminished herbicide discovery efforts. Some of the reduced herbicide discovery research was also due to company consolidations and the availability of more generic herbicides. Another problem might be that the best herbicide molecular target sites may have already been discovered. However, target sites that are not utilized, for which there are inhibitors that are highly effective at killing plants, suggests that this is not true. Results of modern methods of target site discovery (e.g. gene knockout methods) are mostly not public, but there is no evidence of good herbicides with new target sites coming from these approaches. In summary, there are several reasons for a long dry period for new herbicide target sites; however, the relative magnitude of each is unclear. The economic stimulus to the herbicide industry caused by the evolution of herbicide-resistant weeds, especially GR weeds, may result in one or more new modes of action becoming available in the not too distant future.

Isolation of a phytotoxic isocoumarin from Diaporthe eres‐infected Hedera helix (English ivy) and synthesis of its phytotoxic analogs

“…1,2 For the first 50 years of herbicide use, this problem was overcome by the introduction of herbicides with new modes of action about every 3 years; however, no new herbicide mode of action has been introduced in ∼30 years. 3 The need for herbicides with different modes of actions is steadily increasing due to widespread herbicide resistance. One promising approach in the search for novel classes of herbicides is based on secondary metabolites produced by plants and microbes.…”

Introductory Chapter: Actual Issues (Moments) in Herbicide Resistance Weeds and Crops

“…The total area affected, although not estimated, may cover several thousand hectares of crops regularly treated with herbicides in countries such as Australia, Canada and the United States of America, as well as countries in the European Union and South America. Weeds have developed resistance to 23 of the 26 known herbicide sites of action and to 161 different herbicides [8], and no new mode of action has been marketed since 1991 [16].…”

Allelopathy: driving mechanisms governing its activity in agriculture

“…To date, some commercial herbicides derived from plants or microorganisms that have already been introduced onto the market belong to different chemical groups, with entirely novel MeA (Duke et al 2002;Dayan et al 2012). The need for new herbicide MeA should be emphasized for at least three important reasons: (a) no new herbicide MeA were released onto the market within the past two decades; (b) the number of herbicides launched onto the market is decreasing steadily, especially due to registration issues; and (c) limitations of current herbicides due to herbicide-resistant weeds are increasing (Duke 2012). Allelochemicals can improve the potential to discover innovative MeA and can enable the discovery of different chemical moieties.…”