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.

er菜（Amaranthus palmeri S.Watson）的快速生长对及时治理这种杂草构成了挑战。分别在2017年和2018年在加登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，以评估麦草畏对控制≤10、15和30厘米高的棕榈曲霉的功效。，它模仿了三种除草剂施用时间：准时施用（第0天）和1-（第1天）和4-d（第4天）延迟。在R处理后，使用三参数和四参数对数逻辑模型在R处理后4周评估视觉损伤等级和枝条生物量的减少（未经处理的百分比）和死亡率。增加麦草畏剂量增加棕榈棕榈无论在田间研究还是在温室研究中，均不考虑植物高度。结果表明，应用延迟1（15厘米）和4 d（30厘米）导致2-和27倍的增加在麦草畏的有效剂量A. palmeri，分别，在野外条件下。但是，在温室中，对于相同水平的棕榈曲霉防治，麦草畏剂量分别需要增加1倍和2倍以上。同样地，麦草的有效剂量可减少棕榈棕榈芽生物量的50％（GR 50）在田间或温室中麦草畏施用分别延迟1（15 cm）和4 d（30 cm）时，增加了4倍和8倍或1倍和2倍以上。为了了解麦草畏在控制棕榈棕榈树早期生长阶段中提高功效的基础，进行了麦草畏吸收和转运研究。结果表明，随着棕榈棕树高度的增加，麦草畏吸收（7％）和易位（15％）显着降低。因此，麦草畏的吸收和转运增加导致在早期生长阶段改善棕榈曲霉防治的功效增加。