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Abstract
Maize hybrids have different levels of tolerance to the herbicide nicosulfuron, depending on the dose, the environment, the phenological stage of the plant and the timing of nitrogen fertilization, and phytotoxic effects can occur without proper management. There is also limited information on the selectivity of current genetically modified hybrids for other recommended herbicides, such as tembotrione. Thus, the objective of this study was to evaluate the effects of herbicides (tembotrione and nicosulfuron) and the timing of nitrogen fertilization on the yield of maize hybrids. The experimental design was a randomized block design, in a 4 × 2 factorial arrangement, with 4 replicates. The treatments consisted of four treatments [weeding; nicosulfuron + atrazine (20 and 32 + 1250 g ha-1 ai) and tembotrione + atrazine (75.6 + 1250 g ha-1 ai)] and two nitrogen fertilization times (0 and 7 days after application). Maize hybrids P30F53 Leptra, DKB 230PRO3 and KWS 9004PRO2 were assessed in two growing seasons (1st and 2nd harvest) during the 2016/2017 growing season. The percentages of weed control; phytotoxicity at 7, 14 and 21 days after application (DAA); plant height; number of rows per ear; and yield at harvest were evaluated. All herbicides were more effective in controlling weeds at the 1st harvest because of favourable climatic conditions. Nitrogen fertilization can be carried out on the same day as the application of the herbicides nicosulfuron and tembotrione with no reduction in yield for the hybrids P30F53 Leptra, DKB 230PRO3 and KWS 9004PRO2.
Highlights
With the expansion of no-tillage systems (NTS) in recent years, there has been increased adoption of post-emergence chemical weed control
The percentage of weed control was more efficient in the 1st harvest than in the 2nd harvest in all evaluations (Table 2)
The highest weed control efficiency of the herbicide occurred in the 1st harvest owing to adequate water conditions at that sowing time, where the rainfall accumulation from sowing until the application of the herbicides was 161.3 mm and 59.8 mm for the 1st and 2nd harvests, respectively
Summary
With the expansion of no-tillage systems (NTS) in recent years, there has been increased adoption of post-emergence chemical weed control. The selectivity of the herbicides for maize has become essential. There are few herbicide options for post-emergence application and with selectivity for maize. They include glyphosate (in RR® materials), tembotrione, mesotrione, atrazine and nicosulfuron. A 7- to 10-day waiting period is recommended between the application of some herbicides and the application of nitrogen fertilizers (Peixoto & Ramos, 2002; López Ovejero et al, 2003). These recommendations are not always followed in the field. Herbicide and topdressing fertilization are applied on the same day potentially leading to symptoms of phytotoxicity and yield losses
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