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Ecologically Based Weed Management (EbWM)
Enabling and Reinforcing the Approach

Leguizamon Eduardo S.1,*, Royo-Esnal Aritz2, and Torra Joel2

1 Cajaraville, Rosario, República Argentina
2 Department of Agricultural and Forest Science and Engineering, ETSEAFIV-Agrotecnio-CERCA Centre, Universitat de Lleida. Alcalde-Rovira Roure, Lleida, Spain
* Corresponding author

1.0 Introduction

Managing food production systems on a sustainable basis is one of the most critical challenges for the future of humanity. Being fundamentally dependent on the world's atmosphere, soils, water, and genetic resources, these systems provide the most essential ecosystem services on the planet. They are also the largest global consumers of land and water, threats to biodiversity through habitat change, and significant sources of air and water pollution in several regions on Earth (Naylor 2008).

The increase in the world population is necessarily associated with a greater demand for food produced by crops, among other approaches (e.g. reducing food wastes or synthetic food). Currently, there are limited possibilities of achieving crops with superior yields, and incorporating new territories into agriculture is not a realistic option. Under these grounds, it is clear that one factor that favors the increase in crop productivity is the management of species considered pests. In this context, weeds are one of the most important biotic constraints.

During the last 70 years, intensive measures have been taken for crop protection against pests through the widespread use of chemical pesticides in order to reduce the loss of agricultural yield. Although mainly chemical-based, crop protection practices have reduced the overall potential losses of 50% to actual losses of about 30%, with crop losses due to pests still varying from 14% to 35% depending on the considered crop and country (Oerke 2006). Consequences of this massive-intensive chemical use in the agroecosystems are increasingly studied as concerns rocketed all over the world.

Integrated pest management (IPM) was proposed 70 years ago by Stern et al. (1959), who outlined a simple but sophisticated idea of pest control in order to manage insect pests while reducing reliance on synthetic pesticides. Briefly, IPM is based on four elements:

1. Knowledge of the thresholds to determine the need for control
2. Necessary population sampling to determine critical densities (economic damage)
3. The biological control capacity in the system
4. Use of insecticides or selective methods compatible to biological control enhancement (Thill et al. 1991)

Later on, Swanton and Weise (1991) after other precursors, proposed the use of integrated weed management (IWM) as a similar approach for weed management in agroecosystems. IWM was then inspired by IPM, as a long-term management strategy that uses a combination of strategies to reduce the population size of weeds to a tolerable level, being economically affordable and also as a tool to reduce undesired environmental effects of herbicides. However, in most crop production systems, generalized recommendations include just a combination of management tactics (cultural + chemical). After more than 30 years, IWM remains in its infancy, since the implementation of IWM has been poor, with little evidence of its sustainability (e.g. reductions in herbicide use). Moreover, nonchemical methods (mechanical) are often adopted as a means of compensating for reduced herbicide efficacy, due to increasing resistance, rather than as alternatives to herbicides. Reluctance to adopt nonchemical methods may be due not only to a lack of knowledge, but also to a lack of farmer motivation and action and/or risk aversion (Moss 2018). Justifiably, herbicides are often seen as the easiest and still most effective option since their convenience outweighs the increased complexity, costs and management time associated with nonchemical alternatives.

To bring numbers to the statements already said, surveys recently made by crop advisors in Argentina (Satorre 2015) within high technology agricultural entreprises concerning the weed problems they faced in the last decade, revealed the following:

• There is great concern about weeds, considered the main adversity, especially in summer crops.
• Weed management technologies used in the last decades have only been based on herbicides and, surprisingly, they are still led by glyphosate.
• Increasing number of species exhibit a range of herbicide tolerant / resistant responses.
• It is only recently that some farmers (less than 10% acreage) began to include cultural practices (such as cover crops).
• There is a lack of incentives for application of IWM practices and/or pesticides reduction programs.
• 70% of summer crops are planted on short-term leased land, where actions are mostly oriented toward annual productivity, neglecting possible future problems such as contamination or the appearance of herbicide resistant weeds.

Thus, although IWM is frequently advertised/proclaimed as a dominant concept associated to sustainability, the difficulty of evaluating the benefits derived from alternative approaches, ignorance, and/or a low use of available knowledge of weed biology present a severe barrier to changes: up to the present time, a majority of the farmers have failed in a massive implementation of IWM.

Similar results emerged from a recent survey made in the cornbelt from the USA. To elucidate the causes or barriers that prevent huge adoption of IWM, Al-Mamun (2018) identified "failures of institutional context declining government policies, counteracted by multinational private companies as main actors." A further contribution (Wilson et al. 2009a) states that "agrochemical supplier companies impose the massive use of their products through business marketing strategies, preventing producers from being oriented in the use of more sustainable practices," and that a key aspect is that "crop advisors should manage to transmit sufficient trust toward the farmers to be able to address the real problem in a clear and concrete way." For this, it is necessary to create a strong link between the different actors through intensive two-way communication and a greater understanding of the way in which producers perceive this problem (Wilson et al. 2009b). A further issue that should be revised is stewardship programs systematically launched and advertised by the agrochemical industry and also by plant protection sellers and distributors in general, with a rather shallow view in relation to the principles of IWM and advanced available knowledge.

An example on a low-profile marketing campaign was that made about 30 years ago when Roundup-Ready soybeans were launched in Argentina. Adverts in media and in rural roads, boosted the use of the simplest solution to tackle weed problems: just glyphosate. Think of glyphosate in the crops - first in soybeans, then in corn, and later on in cotton and others - plus glyphosate in the fallow. In fact, the tremendous success of direct drilling in Argentina was only possible when two hard technological bottlenecks were overcome: how to place seeds in an undisturbed soil by mouldboard-plough + harrowing (using newly designed planters) and how to get rid of weeds without mechanical tactics (using a novel and very effective herbicide: glyphosate).

Not only companies but also advisors and educators may fail to promote IWM within the frame of farmers' experience and belief structure. Targeted communication efforts that address key misperceptions, and highlight the cost-effective nature of integrated approaches may increase adoption of IWM and ultimately increase sustainability of the agroecosystem. Unfortunately, IWM systems have been perceived as unreliable, resulting in increased risk of weed control failure. The acceptance of IWM by growers will depend on their risk perception of management, individual management capability and environmental interactions that will influence the economic viability of the crop system. The adoption of IWM is usually hindered by the fact that chemical means are often growers' first and only choice, as synthetic herbicides are perceived as an effective, rapid and cost-effective solution for weed management. However, the consequences of intensive pesticide usage in agriculture are now quite well known and fortunately widely and progressively studied, being the increasingly widespread herbicide-resistant weed biotypes as the most striking example of the unsustainability of current plant protection strategies.

1.1 Basis for a Sucessful Ecologically Based Weed Management Approach

In 2008, Bastiaans et al. reflected on the possibilities and limitations of ecological approaches in weed control practices, highlighting the need for research in order to provide clear insight in effectiveness and applicability of the utilization of ecological knowledge translated into practical strategies of weed management. If we do agree that the maintenance of resilience and diversity are key issues for the agriculture to be sustainable (and even more under the intensification process already started), then we should address for a reinforced and enlarged ecologically based weed management (EbWM) definition, backed up by complementary major related disciplines. It must be pointed out that ecology provides the theoretical basis for weed science, much as physics provides a theoretical basis for engineering and biology the theoretical basis for medicine (Liebman...