Selectivity of post-emergent herbicides for weed control in birdsfoot trefoil crops

Abstract Background: Competition with weeds and the lack of selective herbicides registered for birdsfoot trefoil crops affect their development and limit their productivity. Objective: This study aimed to evaluate selectivity of post-emergent herbicides for weed control in birdsfoot trefoil crops. Methods: Experiments were carried out in a greenhouse and on a field, in both vegetative and reproductive development stages of birdsfoot trefoil crops. Treatments were composed of post-emergent herbicides recommended for soybean, corn and garlic cultivation. Phytotoxicity (PHYTO), plant height (HEI), shoot dry matter (SDM) and root dry matter (RDM) were evaluated. Data were submitted to the analysis of variance and when means were significant, they were compared by the Duncan’s Test (p≤0.05). In order to determine post-emergent herbicides which were selective to the crop, those that provided PHYTO below or equal to 15% were recommended, since they did not significantly interfere with morphological variables HEI, SDM and RDM, by comparison with the control. Results: Unlike results found in the vegetative stage, birdsfoot trefoil plants were more tolerant to phytotoxic effects of herbicides imazethapyr, chlorimuron-ethyl, cloransulam-methyl and fomesafen in the reproductive stage. The variables were negatively affected by the herbicides bentazon, glyphosate and carfentrazone-ethyl, with PHYTO higher than 40% at 20 days after treatment in the vegetative stage. Conclusions: Herbicides imazethapyr, chlorimuron-ethyl and flumetsulam, when applied as post-emergent ones, regardless of the development stage of the species, are selective to birdsfoot trefoil crops, without affecting crop development, whereas herbicides cloransulam-methyl and fomesafen are not selective to them.

研究背景：杂草竞争以及缺乏登记用于百脉根（birdsfoot trefoil）作物的选择性除草剂，会影响其生长发育并限制其生产力。研究目的：本研究旨在评估用于百脉根作物田间除草的苗后除草剂的选择性。试验方法：分别在百脉根的营养生长与生殖生长阶段，于温室及大田环境中开展试验。供试药剂为推荐用于大豆、玉米及大蒜种植的苗后除草剂。测定指标包括药害指数（phytotoxicity, PHYTO）、株高（plant height, HEI）、地上部干物质（shoot dry matter, SDM）与地下部干物质（root dry matter, RDM）。数据采用方差分析进行统计检验，若均值差异显著，则采用邓肯氏新复极差检验（Duncan’s Test，p≤0.05）进行多重比较。为筛选对作物具有选择性的苗后除草剂，以药害指数≤15%且与对照组相比未显著干扰株高、地上部干物质及地下部干物质等形态指标的药剂作为入选标准。试验结果：与营养生长阶段的结果不同，百脉根植株在生殖生长阶段对咪唑乙烟酸（imazethapyr）、氯嘧磺隆（chlorimuron-ethyl）、氯酯磺草胺（cloransulam-methyl）以及氟磺胺草醚（fomesafen）的药害耐受性更强。在营养生长阶段施用苯达松（bentazon）、草甘膦（glyphosate）与氟唑草酯（carfentrazone-ethyl）后，施药20天时药害指数均高于40%，对各测定指标产生了负面影响。研究结论：无论百脉根处于哪个生长阶段，苗后施用咪唑乙烟酸、氯嘧磺隆以及氟噻磺草胺（flumetsulam）均对百脉根作物具有选择性，不会影响其生长发育；而氯酯磺草胺与氟磺胺草醚则不具备该选择性。