Chemical management of weeds in cassava crop, cultivar ‘Santa Helena’

ABSTRACT The objective of this study was to evaluate the selectivity of cassava cultivar ‘Santa Helena’ and the efficiency of weed control using herbicides applied alone or tank mixed with and without sequential applications. Two experiments were carried out, both in a randomized block design with four replications. The treatments for the 1st experiment were: Hand hoeing (weed-free control); No hand hoeing (non-weeded control); sulfentrazone (500 g ha-1); sulfentrazone/[clomazone + clethodim] (500/[1125 + 120] g ha-1); sulfentrazone/mesotrione (500/240 g ha-1); S-metolachlor (1920 g ha-1); S-metolachlor/[clomazone + clethodim] (1920/[1125 + 120] g ha-1); S-metolachlor/mesotrione](1920/240 g ha-1); [sulfentrazone + S-metolachlor]/[clomazone + clethodim] ([500 + 1920]/[1125 + 120] g ha-1); [sulfentrazone + S-metolachlor]/mesotrione ([500 + 1920]/240 g ha-1). The treatments of the 2nd experiment were: Hand hoeing (weed-free control); No hand hoeing (non-weeded control); glyphosate (360 g ha-1) + hand hoeing; glyphosate + sulfentrazone (360 + 500 g ha-1); glyphosate + flumioxazin (360 + 50 g ha-1); glyphosate + clomazone (360 + 1125 g ha-1); glyphosate + S-metolachlor (360 + 1920 g ha-1); glyphosate + sulfentrazone + clomazone (360 + 400 + 900 g ha-1); glyphosate + sulfentrazone + S-metolachlor (360 + 400 + 1440 g ha-1); glyphosate + flumioxazin + clomazone (360 + 40 + 900 g ha-1); glyphosate + flumioxazin + S-metolachlor (360 + 40 + 1440 g ha-1). In the first experiment, only the treatments S-metolachlor, S-metolachlor/[clomazone + clethodim] and S-metolachlor/mesotrione did not present efficient weed control, causing reduction in yields; the other treatments were crop selective and efficient. In the second experiment, all treatments showed excellent levels of weed control up to 65 DAA and were crop selective. It is concluded that applications of tank mixtures, sequential mixtures and the use of glyphosate mixed with pre-emergent herbicides constitute excellent alternatives of weed management strategies in ‘Santa Helena’ cassava.

摘要 本研究旨在评估木薯品种‘圣海伦娜（Santa Helena）’的作物选择性，以及采用单施、桶混施，或配合/不配合序贯施药方式的除草剂的除草效果。本研究设置两个试验，均采用随机区组设计，设置4次重复。
第一个试验的处理包括：人工锄草（无杂草对照，即完全除草的对照处理）；不人工锄草（未除草对照，即空白对照）；氟磺草胺（sulfentrazone，500 g ha⁻¹）；氟磺草胺/[异恶草酮（clomazone）+烯草酮（clethodim）]（500/[1125 + 120] g ha⁻¹）；氟磺草胺/硝磺草酮（mesotrione，500/240 g ha⁻¹）；S-异丙甲草胺（S-metolachlor，1920 g ha⁻¹）；S-异丙甲草胺/[异恶草酮+烯草酮]（1920/[1125 + 120] g ha⁻¹）；S-异丙甲草胺/硝磺草酮（1920/240 g ha⁻¹）；[氟磺草胺 + S-异丙甲草胺]/[异恶草酮 + 烯草酮]（[500 + 1920]/[1125 + 120] g ha⁻¹）；[氟磺草胺 + S-异丙甲草胺]/硝磺草酮（[500 + 1920]/240 g ha⁻¹）。
第二个试验的处理包括：人工锄草（无杂草对照）；不人工锄草（未除草对照）；草甘膦（glyphosate，360 g ha⁻¹）+人工锄草；草甘膦+氟磺草胺（360 + 500 g ha⁻¹）；草甘膦+氟烯草酸（flumioxazin，360 + 50 g ha⁻¹）；草甘膦+异恶草酮（360 + 1125 g ha⁻¹）；草甘膦+S-异丙甲草胺（360 + 1920 g ha⁻¹）；草甘膦+氟磺草胺+异恶草酮（360 + 400 + 900 g ha⁻¹）；草甘膦+氟磺草胺+S-异丙甲草胺（360 + 400 + 1440 g ha⁻¹）；草甘膦+氟烯草酸+异恶草酮（360 + 40 + 900 g ha⁻¹）；草甘膦+氟烯草酸+S-异丙甲草胺（360 + 40 + 1440 g ha⁻¹）。
第一个试验中，仅S-异丙甲草胺、S-异丙甲草胺/[异恶草酮+烯草酮]及S-异丙甲草胺/硝磺草酮这三个处理未实现高效除草，进而导致木薯产量降低；其余处理均对作物具有选择性且除草效果优异。
第二个试验中，所有处理在施药后65天（Days After Application, DAA）内均表现出极佳的除草效果，且对作物安全无药害。
综上，桶混施药、序贯施药以及草甘膦与芽前除草剂混用的方案，均可作为‘圣海伦娜’木薯田杂草管理的优秀备选方案。