Split application of glyphosate in herbicide-tolerant maize provides efficient weed control and favors beneficial epigeic arthropods

Abstract

Wide deployment of genetically modified herbicide-tolerant (GMHT) maize may affect the efficiency of weed control methods and impair ecosystem functioning. We examined these potential threats using glyphosate-tolerant maize NK603 (Monsanto Technology LLC, St. Louis, MO, USA) planted in 54 randomly distributed plots in 2013 and 2014. Maize was grown in three herbicide treatments combined with six tillage regimes. Conventional, single post-emergence application of a selective herbicide MaisTer (Bayer CropScience GmbH, Frankfurt am Main, Germany; hereafter as MT) was compared with two herbicide strategies used in the glyphosate-tolerant crops: split application of Roundup Rapid (Monsanto Europe S.A./N.V., Brussels, Belgium; hereafter as RRRR) and application of this herbicide mixed with the soil residual herbicide Guardian Extra (Monsanto Europe S.A./N.V.; hereafter as RRGE). MT proved unreliable, whereas RRRR and especially RRGE provided efficient weed control and affected weed performance during the season. RRRR permitted restoration of weed cover during the latter half of the cultivation season. Conventional, reduced, and conservation (mulching with Hordeum vulgare, Phacelia tanacetifolia, Sinapis alba, and Trifolium incarnatum) tillage had minor effect on the weed performance. Carabids, staphylinids, and spiders were monitored to assess environmental impact of tested weed management practices. Carabid communities were not affected by the type of tillage but responded to the herbicide treatments. The plots treated with MT harbored the highest carabid activity abundance and species richness, followed by RRRR, and then by RRGE. RRRR and RRGE treatments also reduced the rise of staphylinid abundance and species richness after harvest, while conventional tillage negatively affected staphylinids at the start of the cultivation season. Spider and carabid activity abundance was similar, but spider species richness was highest in the RRRR plots. Neither herbicides nor tillage strongly affected arthropod species evenness. Multivariate analysis showed that weed species richness was significantly correlated with the species activity abundance of all three arthropod groups; weed coverage had a similar but smaller effect but the effect of herbicides and tillage was negligible. We concluded that herbicide treatments curbed weed performance which consequently influenced associated arthropods.The RRRR herbicide treatment adequately regulates weeds and exerts restoration of weed cover later in growing season that is beneficial to the arthropods. Thus, GMHT crops have a potential to combine economic and environmental advantages for agroecosystem sustainability and can be recommended for implementation in European crop production systems.