Abstract
ABSTRACT The application of glyphosate associated with other herbicides is an important alternative for weed control in maize, to increase control spectrum and to minimize problems with resistance and tolerance from some species to the product. The objective of this work was to evaluate the efficacy, selectivity and effects on the grain yield components of glyphosate-resistant maize as a function of its application, associated or not with other pre- and postemergence herbicides. The design used was randomized blocks with four replications. Treatments consisted in the use of glyphosate combined with the herbicides: atrazine, [atrazine + simazine], [atrazine + oil], [atrazine + S-metolachlor], applied pre- and/or postemergence and [nicosulfuron + mesotrione] only postemergence, plus two controls, one weeded and one infested. The evaluated variables were maize phytotoxicity, weed control, ear insertion height, number of rows per ear, number of grains per row, one thousand grain mass and grain yield. Herbicide treatments caused low phytotoxicity to maize, less than 6%; control greater than 88, 95 and 95% for alexandergrass, turnip and sunflower, respectively, and did not affect grain yield components. The tested herbicides are selective to the hybrid Forseed 2A521 PW and effective in weed control. Weed control with weeding or herbicide increased maize Forseed 2A521 PW yield by 43%. The association of glyphosate with pre- or postemergence herbicides increased maize grain yield by approximately 14%.
Highlights
Maize is one of the main crops sown in Brazil, it is used in human and animal feed, being cultivated throughout the national territory
At this time of evaluation, the treatments used in preemergence, S-metolachlor + glyphosate and [atrazine + S-metolachlor] + glyphosate and in postemergence S-metolachlor + glyphosate and glyphosate + [nicosulfuron + mesotrione] were the second group of herbicides that caused the highest levels of phytotoxicity to maize
At 21 DAT, the crop no longer presented injuries resulting from the use of herbicides, in other words, the plants recovered from the initial symptoms (Table 3)
Summary
Maize is one of the main crops sown in Brazil, it is used in human and animal feed, being cultivated throughout the national territory. The sown area in 2017/2018 crop was approximately 17.3 million hectares, with a production of about 90 million tonnes (CONAB, 2019). Despite the large volume of grains produced, the average yield is low, ranging from 4 to 5 t·ha-1. Among the factors that favor the low productivity of maize grains, the inadequate management of the weed community can be mentioned, because these weeds compete for the available resources in the environment, besides being hosts of insects and diseases or even release allopathic substances that interfere in the growth and development of the crop. The absence of control may cause losses higher than 80% in crop yield (GALON et al, 2018a)
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