Evidence that organic farming promotes pest control, Muneret et al. 2018

Citing the problems posed globally by pesticide use and farmland expansion, this study looks at the potential of organic farming, seen as a popular prototype of ecological intensification, to limit pest infestations. Ecological intensification “is based on optimizing the ecological functions that support ecosystem services to increase the productivity of agro-ecosystems” [Muneret 2018: 361], and thus serves as a framework for evaluating farming system changes that could handle both ecological stress/collapse and human population growth. “Organic farming is a certified production system based on the principle of using farming practices that are expected to enhance ecological processes while prohibiting the use of external synthetic inputs” [Muneret 2018: 361].

Our findings in particular show that organic farming practices are able to match or outperform conventional pest control practices against pathogens and animal pests [such as insects] whereas weeds are much more abundant in organic than in conventional systems. Thus, ecological intensification based on organic farming can contribute to the control of animal pests and pathogens by enhancing biological control services and limiting their infestation levels [Muneret 2018: 365].

Whereas conventional pest control emphasizes top-down control with pesticide, ecological pest control is achieved through multiple processes:

Once established, pest populations within agro-ecosystems are affected, to varying degrees, by three ecological processes: bottom-up effects mediated by soil or plant communities involving, for instance, plant quality or habitat structure, horizontal processes within a given trophic level such as competition for resources between individuals or populations, and top-down control by natural antagonists such as predation or parasitism [Muneret 2018: 363].

Given the benefits of biodiversity for enhancing these three ecological effects, the authors explain that weeds, which are not as well suppressed in organic systems, may actually be beneficial in terms of limiting infestation by animals/insects and pathogens.

Our analysis shows that organic farming results in much higher weed infestation. This result is supported by previous studies that have shown higher abundance and diversity of plant communities within organic arable fields. We assume that this higher weed infestation, in turn, most likely influences animal pest and pathogen populations. These bottom-up effects of plant communities on higher trophic levels have been demonstrated and more abundant or diverse plant communities have been found to limit insect and disease infestation through direct and indirect mechanisms because of higher structural complexity or lower habitat quality under increased plant diversity. Although this needs further investigation, the observed performance of organic farming on animal pest and pathogen infestation may result from bottom-up effects generated by the higher weed infestation levels in organic cropping systems [Muneret 2018: 364].

Although the authors didn’t examine the effects of pest infestations on yield, they note that previous studies have suggested that weeds do not necessarily result in crop yield reductions in organic systems.