Abstract
ABSTRACT Soil residues following the application of 2,4-D and dicamba for weed control may delay the establishment and initial development of soybean, but rainfall can reduce the interval required between application and sowing. Rainfall volumes (0; 10; 30; 60; and 90 mm) were simulated following the application of 2,4-D (300 and 600 g a.e. ha-1) and dicamba (120 and 240 g a.e. ha-1), and the effects on soybean were evaluated. The application of 2,4-D did not affect the soybean establishment or initial development, regardless of the simulated rainfall volume. However, the dicamba residual reduced the soybean establishment for the lower rainfall volumes. Phytotoxicity was more severe for the highest dicamba rate (75-100 %), being 50-100 % for the lowest rate. The higher volumes of simulated rainfall reduced the phytotoxicity of dicamba in soybean, but were not sufficient to reduce the deleterious effects on the initial development of the crop.
Highlights
In order to manage glyphosate-resistant broadleaf weeds in soybean, one of the most efficient and usual strategies employed by producers is the preplant application of synthetic auxin in tank mixes or the sequential application with others herbicides
It is important to note that the irrigation conditions after the soybean planting presumably favored a maximum herbicide dissipation, since 2,4-D is degraded via hydrolysis and oxidation in wet conditions (Cessna et al 2017)
The preplant application of 2,4-D at any rate had no adverse effects on the soybean phytotoxicity, regardless of the amount of simulated rainfall (Figures 2A and 2B)
Summary
In order to manage glyphosate-resistant broadleaf weeds in soybean, one of the most efficient and usual strategies employed by producers is the preplant application of synthetic auxin in tank mixes or the sequential application with others herbicides. Dicamba and 2,4-D are commonly tankmixed with glyphosate in preplant soybean, and provide an excellent control of glyphosate-resistant or tolerant weeds, such as Conyza spp., Richardia brasiliensis, Commelina benghalensis and Ipomoea nil with up to 12 leaves (Osipe et al 2017). These herbicides are considered post-emergent, and preplant applications are restricted to a certain interval before the soybean planting. The degradation of these herbicides is influenced by microbial activity and soil temperature (Comfort et al 1992)
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