The Current Status of Weed Resistance to Herbicides and The Discovery of New Herbicides With Novel Modes of Action Necessary to Combat Them

Abstract

In 2016 and after retiring from a fulltime career in Herbicide Research and Development, I wrote an article for Outlooks addressing the question ‘Can we expect new herbicides with novel modes of action in the foreseeable future?’ and I would like to use this editorial to investigate if we are any closer to answering this question which is important because of the increasing problems of weeds evolving resistance to existing herbicides. Weed management is still essential to maximise crop yields in agriculture. Yield losses of up to 40% across the major global food crops can occur without effective weed control, due to competition between the weeds and crops for nutrients and light, as well as interfering with crop harvest and quality. Herbicides are essential tools in integrated weed management (IWM) but their effectiveness is being eroded due to widespread weed resistance, in part due to overuse of the limited number of herbicide products currently available to the grower. Cultural methods for control of weeds such as, changing rotations, use of cover crops; deep ploughing; manual removal of weeds and chemical mulching are clearly part of the IWM toolbox. However, deep ploughing (and any type of physical disturbance of soil) and chemical mulching, whilst potentially effective, are not applicable throughout global crop production and also are not sustainable environmentally friendly options. Similarly, other non-chemical methods, such as electro-physical and heat treatments including high energy light, boiling water, steam, fire, flame weeding and hot foam have been sold as having potential to replace herbicides, but I question their suitability in main stream row-crop agriculture and also the environmental impact of their use, particularly if they would be regulated as herbicides and needed the extensive catalogue of ecotoxicology studies to investigate adverse effects on non-target organisms and environmental fate studies. Biological approaches are receiving increasing interest in pest management for control of diseases and insects, but these appear not to be an option for weed control.