Abstract
The use of soybean varieties resistant to the herbicides dicamba and 2,4-D may lead to drifts towards areas grown with non-resistant varieties. The aim of this study was to evaluate the effects of dicamba and 2,4-D underdoses applied at the phenological stages V4 and R2 of soybeans. Two experiments were conducted with dicamba or 2,4-D in a randomized block design with four replications. The 4 × 2 + 1 factorial scheme was composed of four doses (0.028, 0.28, 2.8, and 28 g ae ha−1) of dicamba or 2,4-D applied at two phenological stages (V4 and R2) + a control treatment (without herbicide application). Dicamba underdoses caused damage to soybean crop affecting its vegetative growth and yield; the injuries caused by 2,4-D were neither enough to damage crop nor affect yield components. Dicamba underdoses applied at V4 caused injuries of up to 41%, while in R2 they reached 70%. Plant height decreased by up to 61% when treated with dicamba. Soybean yield was reduced by 29 and 76% when the simulated drift occurred at V4 and R2, respectively, and at a dose of 28 g ae ha−1 of dicamba. For the tested underdoses, only 2,4-D had no effect in soybean crop yield.
Highlights
The emergence of glyphosate-resistant eudicotyledonous weed species led to the need to seek alternative control measures such as the insertion of varieties resistant to the herbicides dicamba (BEHRENS et al, 2007) and 2,4-D (WRIGHT et al, 2010), which may be part of a management program for herbicide-resistant plants commonly used
The treatments were arranged in a 4 × 2 + 1 factorial scheme of four underdoses (0.028, 0.28, 2.8, and 28 g ae ha−1) applied at two soybean phenological stages (V4 and R2), plus an additional treatment without herbicide application
The induced injuries varied according to the herbicide, doses, and soybean phenological stage at application time (Table 1)
Summary
The emergence of glyphosate-resistant eudicotyledonous weed species led to the need to seek alternative control measures such as the insertion of varieties resistant to the herbicides dicamba (BEHRENS et al, 2007) and 2,4-D (WRIGHT et al, 2010), which may be part of a management program for herbicide-resistant plants commonly used. The drift of these herbicides on non-resistant soybean plants can cause damage to the vegetative and reproductive development of the crop, reducing its yield. Underdoses of auxin herbicides can cause abnormalities in sensitive eudicotyledonous plants (SILVA et al, 2018). The contamination of the spraying equipment, spraying drift, and volatilization of dicamba can cause phytotoxicity and reduce soybean yield (GROWE, 2017). Drift is the deviation of the trajectory of particles released during the application, which do not reach the target and cause product losses (SOUZA; CUNHA; PAVANIN, 2011) and economic and environmental damages in nearby areas. Even after the herbicides reach the target, there is still a risk of drift due to their volatilization (JONES, 2018), as well as contamination of sprayer tanks by them
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