New tools are being developed to limit the use of herbicides in crops and improve the efficacy of alternative management methods. An update.
The tool currently recommended to farmers to help them manage weeds in crops is the “economic weed threshold”: beyond a certain weed density, herbicide intervention is considered to be less costly than the losses otherwise incurred. This tool is useful for identifying the individual harmfulness of weed species, but on its own does not permit sustainable and optimal management of weed flora. For that, preventive and curative measures are essential, applied at the scale of each crop and rotation, and based on the principles of integrated plant protection. The implementation of these measures requires new decision-support tools based on criteria other than weed density, to enable farmers to manage weeds with the lowest amount of herbicides possible.
Relevant alternative indicators
New indicators have been developed which are now being used by researchers to improve harmfulness evaluation. The most pertinent of these are the period of weed emergence compared to the growing stage of the crop, total and per-species weed cover, and total and per-species weed biomass. The challenge now is to be able to use these indicators in practice, in a simplified but reliable form. Agroscope’s weed science research group is currently developing a visual method for estimating the volume of weeds, which should be amenable to improvement with the aid of the new imaging technologies.
Next stage: designing models
The next stage in providing decision-support tools to farmers is to design models suitable for sustainable weed management. The FLORSYS model developed by the INRAE already allows researchers to evaluate the effect of cropping systems on weeds and yield on a virtual plot over several years. Work is still in progress to incorporate the results of this model into a simpler, faster decision-support tool intended for farmers.
- ‘Economic weed thresholds’ are useful for identifying the individual harmfulness of species, but do not permit sustainable and optimal management of weed flora on their own.
- Weed density is not an adequate indicator for explaining harmfulness. Other indicators exist, and methods are being developed to enable their use in practice.
- Modelling the effects of cropping systems on weed flora and yield is the basis for the development of powerful decision support tools.