Abstract
ABSTRACT: Efficient management of sourgrass is one of the main challenges faced by Brazilian soybean farmers. Biological and ecological characteristics of this weed, as well as wide distribution of glyphosate-resistant biotypes, make it difficult to control this species. The objective of this work was to estimate interference of sourgrass in soybean yield. Seven experiments were conducted during three consecutive years (2012/2013, 2013/2014 and 2015/2016 cropping seasons); six of them were on-farm trials where sourgrass infestation was mainly originated from clump regrowth, while infestation originated from seeds in one trial. Data from all sites and experiments were submitted to a combined analysis, according to the study factors and variables, to determine the greatest number of information points for the variable under each circumstance. To each data set, a 1st degree polynomial regression was fit, with a 95% confidence interval. The degree of sourgrass interference varies according to plant origin (seed or clump regrowth) but, in both cases, yield losses are directly correlated with sourgrass densities, aboveground dry mass accumulation and soil coverage. Plants coming from clumps tend to cause higher yield losses than those originated from seeds. These data highlight the importance of performing proper management of sourgrass, especially in its initial stages of development, in view of the high level of losses that perennial plants can cause to crops.
Highlights
Brazil is the second largest soybean producer in the world, with an estimated area of 33.91 million hectares in the 2016/2017 cropping season, and a net production volume of 115 million tons (Conab, 2017).Weed interference in soybean can account for as much as 90% of losses in grain yield if no effective control method is used (Silva et al, 2009a)
Among the weeds with increasing importance in soybean production systems, sourgrass (Digitaria insularis) is one of the main challenges currently faced by South American farmers (Lopez Ovejero et al, 2017)
As a result of its perennial growth habit, plants growing during the period between harvest and sowing of subsequent crops usually form large clumps
Summary
Brazil is the second largest soybean producer in the world, with an estimated area of 33.91 million hectares in the 2016/2017 cropping season, and a net production volume of 115 million tons (Conab, 2017).Weed interference in soybean can account for as much as 90% of losses in grain yield if no effective control method is used (Silva et al, 2009a). Among the weeds with increasing importance in soybean production systems, sourgrass (Digitaria insularis) is one of the main challenges currently faced by South American farmers (Lopez Ovejero et al, 2017). This weed is considered to be a hard-to-control species, because of its ability to reproduce both by seeds and rhizomes, adaptability to germinate and grow in a wide range of light and temperature conditions, and the widespread selection of glyphosate-resistant biotypes (Machado et al, 2006; Mondo et al, 2010; Carvalho et al, 2011; Mendonça et al, 2014; Gilo et al, 2016). New reports of glyphosate-resistant biotypes have spread throughout the central region of Brazil, mainly in grain-producing areas, most likely because of farm machinery movement, wind-mediated dispersal (Lopez Ovejero et al, 2017) and local selections (Takano et al, 2018)
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