Impact of new management practices on arable and field margin plant communities in sunflower, with an emphasis on the abundance of Ambrosia artemisiifolia (Asteraceae)

Abstract

Some troublesome weeds such as Ambrosia artemisiifolia have led farmers to adopt herbicide‐tolerant varieties (HTVs) in cultivated sunflower fields. Agricultural practices associated with the use of HTVs have raised concerns among public authorities, prompting the recommendation to monitor the potential effects of HTVs on biodiversity. In this context, we surveyed the vegetation of 239 sunflower fields and their margins in three French regions between 2017 and 2019, with a specific focus on A. artemisiifolia. We collected information on 21 explanatory variables covering agricultural practices, landscape factors, and spatiotemporal data. Herbicide‐tolerant varieties fields were associated with lower weed diversity but similar field margin community diversity. This lower weed diversity can be attributed to the greater use of herbicides and shorter crop rotations, whereas landscape factors may be more important for the diversity in field margins. Conventional fields with traditional varieties showed lower abundance of A. artemisiifolia compared with organic fields and HTV fields. A. artemisiifolia abundance was higher in the most infested region, in fields with a high proportion of sunflower crops in the crop rotation, late sowing dates, high numbers of hoeing operations, and high numbers of post‐emergence treatments. We interpreted the association of hoeing and HTV use with a high abundance of A. artemisiifolia as a response to weed infestation rather than its cause. In conclusion, no unintended effects of HTVs were found in field margins, but practices associated with HTVs lead to lower weed community diversity and HTV fields had still high A. artemisiifolia abundance after weed control.

Herbicide control of Ambrosia artemisiifolia in sunflower, soybean and maize

“…When plants with mature seeds are mown, A. artemisiifolia spreads via the seeds (Odero et al 2018). The powerful techniques of integrated weed management are harvest weed seed control (HWSC), winter cover, and late planting (Beam et al 2021) or the use herbicide-tolerant varieties e.g., in cultivated sunflower fields (Reisinger et al 2013;Fried et al 2022), soybean, maize (Burke et al 2008;Nandula 2019) or in rice (Chen et al 2021). HWSC is an evolving method to catch, destroy or remove weed seeds during or after crop harvest (Borger et al 2021).…”

Weed communities are more diverse, but not more abundant, in dense and complex bocage landscapes

“…Marshall, 1989; Metcalfe et al, 2019). Plant spillover could extend over larger areas under organic farming given the absence of herbicide and chemical fertilizer treatments (Fried et al, 2022), but studies are lacking. Further, plant spillover is associated with an increased proportion of ‘transient’ species in arable fields (Metcalfe et al, 2019).…”