Abstract Rapid growth of Palmer amaranth (Amaranthus palmeri S. Watson) poses a challenge for timely management of this weed. Dose–response studies were conducted in 2017 and 2018 under field and greenhouse conditions near Garden City and Manhattan, KS, respectively, to evaluate the efficacy of dicamba to control ≤10-, 15-cm, and 30-cm-tall A. palmeri, which mimics three herbicide application timings: on-time application (Day 0) and 1- (Day 1) and 4-d (Day 4) delays. Visual injury rating and reduction in shoot biomass (% of nontreated), and mortality were assessed at 4 wk after treatment using a three- and four-parameter log-logistic model in R. Increasing dicamba doses increased A. palmeri control regardless of plant height in both the field and greenhouse studies. The results suggest that delaying application 1 (15 cm) and 4 d (30 cm) resulted in 2- and 27-fold increases in the effective dose of dicamba on A. palmeri, respectively, under field conditions. However, in the greenhouse, for the same level of A. palmeri control, more than 1- and 2-fold increases in dicamba dose, respectively, were required. Similarly, the effective dose of dicamba required for 50% reduction in A. palmeri shoot biomass (GR50) increased more than 4- and 8-fold or more than 1- and 2-fold when dicamba application was delayed by 1 (15 cm) and 4 d (30 cm), in the field or in the greenhouse, respectively. To understand the basis of increased efficacy of dicamba in controlling early growth stages of A. palmeri, dicamba absorption and translocation studies were conducted. Results indicate a significant reduction in dicamba absorption (7%) and translocation (15%) with increase in A. palmeri height. Therefore, increased absorption and translocation of dicamba results in increased efficacy in improving A. palmeri control at early growth stages.

中文翻译：

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增加的吸收和易位有助于提高麦草畏控制早期生长阶段的苋菜 (Amaranthus palmeri) 的功效

摘要 苋菜（Amaranthus palmeri S. Watson）的快速生长对这种杂草的及时管理提出了挑战。分别于 2017 年和 2018 年在花园城和堪萨斯州曼哈顿附近的田间和温室条件下进行了剂量反应研究，以评估麦草畏控制≤10、15 厘米和 30 厘米高的 A. palmeri 的功效，模拟三种除草剂施用时间：按时施用（第 0 天）和 1-（第 1 天）和 4-d（第 4 天）延迟。使用 R 中的三参数和四参数对数逻辑模型在处理后 4 周评估视觉损伤评级和芽生物量的减少（未处理的百分比）和死亡率。增加麦草畏剂量增加了 A. palmeri 控制，而不管植物高度在田间和温室研究中。结果表明，在田间条件下，延迟施用 1 (15 cm) 和 4 天 (30 cm) 导致麦草畏对 A. palmeri 的有效剂量分别增加 2 倍和 27 倍。然而，在温室中，对于相同水平的 A. palmeri 控制，需要将麦草畏剂量分别增加 1 倍和 2 倍以上。类似地，当麦草畏施用延迟 1 (15 cm) 时，使 A. palmeri 枝条生物量 (GR50) 减少 50% 所需的麦草畏有效剂量增加了 4 倍和 8 倍以上或 1 倍和 2 倍以上和 4 天（30 厘米），分别在田间或温室中。为了了解麦草畏在控制 A. palmeri 早期生长阶段的功效增加的基础，进行了麦草畏吸收和易位研究。结果表明，随着麦草畏高度的增加，麦草畏的吸收 (7%) 和易位 (15%) 显着降低。因此，麦草畏吸收和易位的增加导致在早期生长阶段提高对麦草畏的控制效果。