The adoption of dicamba-tolerant crops has reduced the challenge of controlling glyphosate-resistant Amaranthus palmeri in these crops. However, introducing herbicide programmes with new mechanisms of action and different intensities can favour major shifts in weed communities. This can affect not only the functionality of the agroecosystem, but also resource availability to the most problematic species. The objectives of this work were to evaluate how herbicide programme structure and intensity affect (a) weed diversity, (b) population growth rate (λ) of weed species and (c) weed community structure based on λ dynamics in a dicamba-tolerant cotton monoculture. To achieve these objectives, a cotton field experiment was established to compare four herbicide programmes from 2011 to 2018. The herbicide programmes differed in the first 4 years (i.e. glyphosate every year, alternating glyphosate and glyphosate plus dicamba every other year, glyphosate plus dicamba every year, and residual herbicide and glyphosate plus dicamba every year). During the last 4 years, all programmes received glyphosate plus dicamba. The weed seedbank was evaluated every spring and λ calculated. Environmental variation from year to year was more important in determining weed richness than herbicide programmes, which exhibited similar richness across all treatments during the eight years of the study. Regardless of herbicide programme, most species maintained λ between zero and one. Only a few species were the exception with λ values above one, such as A. palmeri, Mollugo verticillata and Eleusine indica. Although glyphosate plus dicamba reduced λ for several species, this herbicide mix was less effective in reducing λ for other weeds compared with glyphosate alone, suggesting a potential antagonism that could change weed community composition. The limited changes in λ for most species suggest the capacity of weeds to adjust reproduction and survival to overcome changes in mortality rates caused by increases in herbicide use intensity.

中文翻译：

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杂草种类的种群增长率对除草剂计划强度的响应及其对杂草群落的影响

采用耐麦草畏作物减少了控制抗草甘膦苋菜的挑战在这些作物中。然而，引入具有新作用机制和不同强度的除草剂计划可能有利于杂草群落的重大转变。这不仅会影响农业生态系统的功能，还会影响最有问题的物种的资源可用性。这项工作的目的是评估除草剂计划的结构和强度如何影响 (a) 杂草多样性、(b) 杂草物种的种群增长率 (λ) 和 (c) 基于 λ 动态的麦草畏棉花中的杂草群落结构单一栽培。为实现这些目标，建立了棉花田间试验以比较 2011 年至 2018 年的四种除草剂计划。除草剂计划在前 4 年有所不同（即每年使用草甘膦，每隔一年交替使用草甘膦和草甘膦加麦草畏，草甘膦加麦草畏每年，残留除草剂和草甘膦加麦草畏每年）。在过去的 4 年中，所有项目都接受了草甘膦加麦草畏。每年春季评估杂草种子库并计算λ。在确定杂草丰富度方面，每年的环境变化比除草剂计划更重要，在八年的研究中，所有处理都表现出相似的丰富度。不管除草剂计划如何，大多数物种的 λ 保持在 0 和 1 之间。只有少数物种例外，其中 λ 值大于 1，例如 在确定杂草丰富度方面，每年的环境变化比除草剂计划更重要，在八年的研究中，所有处理都表现出相似的丰富度。不管除草剂计划如何，大多数物种的 λ 保持在 0 和 1 之间。只有少数物种例外，其中 λ 值大于 1，例如 在确定杂草丰富度方面，每年的环境变化比除草剂计划更重要，在八年的研究中，所有处理都表现出相似的丰富度。不管除草剂计划如何，大多数物种的 λ 保持在 0 和 1 之间。只有少数物种例外，其中 λ 值大于 1，例如一个。palmeri、Mollugo verticillata和Eleusine indica。尽管草甘膦加麦草畏降低了几个物种的 λ，但与单独的草甘膦相比，这种除草剂混合物在降低其他杂草的 λ 方面效果较差，这表明可能会改变杂草群落组成的潜在拮抗作用。大多数物种的 λ 变化有限，表明杂草有能力调整繁殖和存活，以克服除草剂使用强度增加引起的死亡率变化。