Weed control of paraquat can be erratic and may be attributable to differing species sensitivity and/or environmental factors for which minor guidance is available on commercial labels. Therefore, the objectives of this research were to quantify selectivity of paraquat across select weed species and the influence of environmental factors. Experiments were performed under controlled conditions in the greenhouse and growth chamber. Compared with purple deadnettle (dose necessary to reduce shoot biomass by 50% = 39 g ai ha−1), waterhemp, Palmer amaranth, giant ragweed, and horseweed were 4.9, 3.3, 1.9, and 1.3 times more sensitive to paraquat, respectively. The injury progression rate over 3 d after treatment (DAT) was a more accurate predictor of final efficacy at 14 DAT than the lag phase until symptoms first appeared. For example, at the 17.5 g ha−1 dose, the injury rate of waterhemp and Palmer amaranth was, on average, 3.6 times greater than that of horseweed and purple deadnettle. The influence of various environmental factors on paraquat efficacy was weed specific. Applications made at sunrise improved control of purple deadnettle over applications at solar noon or sunset. Lower light intensities (200 or 600 μmol m−2 s−1) surrounding the time of application improved control of waterhemp and horseweed more than 1,000 μmol m−2 s−1. Day/night temperatures of 27/16 C improved horseweed and purple deadnettle control compared with day/night temperatures of 18/13 C. Though control was positively associated with injury rates in the application time of day and temperature experiments, a negative relationship was observed for waterhemp in the light-intensity experiment. Thus, although there are conditions that enhance paraquat efficacy, the specific target species must also be considered. These results advocate paraquat dose recommendations, currently based on weed height, be expanded to address sensitivity differences among weeds. Moreover, these findings contrast with paraquat labels stating temperatures of 13 C or lower do not reduce paraquat efficacy.

中文翻译：

---

将受环境条件影响的选定杂草物种的初始百草枯损伤与最终功效联系起来

百草枯的杂草控制可能不稳定，可能是由于不同的物种敏感性和/或环境因素造成的，商业标签上提供的指导很少。因此，本研究的目的是量化百草枯对特定杂草的选择性以及环境因素的影响。实验在温室和生长室的受控条件下进行。与紫荆花相比（减少 50% 枝条生物量所需的剂量 = 39 g ai ha-1)、水麻、苋菜、巨型豚草和马草对百草枯的敏感性分别高出 4.9、3.3、1.9 和 1.3 倍。与直到症状首次出现的滞后期相比，治疗后 3 d 的损伤进展率 (DAT) 是 14 DAT 最终疗效的更准确预测指标。例如，在 17.5 g ha-1剂量下，水麻和苋菜的致伤率平均是马鞭草和紫荆的3.6倍。各种环境因素对百草枯功效的影响是杂草特异性的。在日出时进行的应用比在太阳正午或日落时的应用改进了对紫色死针的控制。较低的光强度（200 或 600 μmol m-2s-1) 在施用时间前后改善了对超过 1,000 μmol m 的水麻和马草的控制-2s-1. 与 18/13 C 的昼/夜温度相比，27/16 C 的昼/夜温度改善了马草和紫荆的控制。虽然在白天和温度实验的应用时间中，控制与伤害率呈正相关，但观察到负相关用于光强度实验中的水麻。因此，尽管存在增强百草枯功效的条件，但也必须考虑特定的目标物种。这些结果提倡扩大目前基于杂草高度的百草枯剂量建议，以解决杂草之间的敏感性差异。此外，这些发现与说明温度为 13 摄氏度或更低的百草枯标签形成对比，并不会降低百草枯的功效。