Efeito de herbicidas pré-emergentes no algodoeiro e período crítico de interferência de plantas daninhas

Abstract

The cotton crop is one of the main agricultural commodities in Brazil. Most cotton cultivars available to growers are resistant to glyphosate and glufosinate herbicides, which, depending on the frequency of use, can result in increased weed resistance to these herbicides. Therefore, the use of pre-emergence herbicides can be a management tool to avoid weed resistance to post-emergence herbicides. Thus, this work aimed to: 1) identify the critical period of weed interference and 2) evaluate weed control with pre-emergence herbicides in cotton. Two experiments were conducted at Fazenda Bonito, in the municipality of Riolândia-SP (19º 57’ 54.6” S 49º 36’ 50.9” W, average altitude of 440 meters), in the 2020/2021 season. In the first experiment, the critical period of weed interference with manual control (planting) was determined, occurring at 7, 14, 21, 28, 35, 42 and 50 days after sowing. The second experiment consisted of the application of pre-emergence herbicides: S-metolachlor, diuron, trifluralin, oxyfluorfen, clomazona, clomazona + diuron, pedimentalin, acetochlor, diuron + trifluralin and the control, using a manual sprayer pressurized with CO2. Cotton, cultivar FM 911 GLTP, was planted in a conventional tillage system with subsoiling, heavy harrowing and light harrowing. Each plot was demarcated 3.2 m wide (4 cotton lines) and 8 m long. Data were collected from the 2 central lines. The evaluations included weed biomass, cotton plant height, production components (number of bolls and average boll weight), fiber yield and fiber productivity, and fiber quality parameters such as length, micronaire, strength and maturity by the HVI (High Volume Instrumentals) method. Data were subjected to analysis of variance and means were compared by Tukey's test at 5% probability. The results showed that the use of pre-emergence provided weed control, not interfering with the number of nodes, height, plant density and fiber quality of cotton, demonstrating that all treatments can be used in weed management. Trifluralin had a higher control efficiency, obtaining the highest score and the lowest weed biomass, contributing to higher cotton productivity. In conclusion, in the period of weed interference, the presence of treatment with pre-emergence contributed to their control, resulting in lower biomass and higher productivity compared to the unclear without pre-emergence.