Monochoria vaginalis (Burm. f.) Kunth is an annual weed commonly found in paddy fields. Understanding the effects of M. vaginalis on the yield and economics of paddy rice (Oryza sativa L.) is essential for integrated weed management. Here, a field experiment was conducted over two consecutive years (2017–2018) to determine the effects of different densities of M. vaginalis (0, 1, 4, 8, 12, 16, 20, and 24 plants m^–2) on yield losses, economic thresholds, and gross returns in paddy rice. The results showed that a higher density of M. vaginalis exhibited greater inhibitory effects on plant height, tiller number per plant, and adjusted gross returns in both early and late rice. The inhibitory effects on spike number per plant, filled grains per panicle, and 1,000-kernel weight were also significant, although lesser than those observed on the other yield traits. The economic threshold of M. vaginalis under manual weeding varied from 2.80 to 4.44 plants m^–2, whereas the threshold levels under herbicide application ranged between 0.71 and 1.03 plants m^–2 in the 2 yr. Averaged across all other factors, the adjusted gross returns decreased by 45.0% with increasing M. vaginalis density from 0 to 24 plants m^–2. Taking into account the economic thresholds and gross returns, irrational use of herbicides should be prevented for weed management in paddy fields. This study provides useful data for reducing the use of chemical herbicides, saving the costs of weed management practices, and protecting the environment of farmland ecosystems.

中文翻译：

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Monochoria阴道密度对水稻（Oryza sativa L.）产量损失、经济阈值和总收益的影响

Monochoria spatialis (Burm. f.) Kunth 是一种常见于稻田的一年生杂草。了解阴道分枝杆菌对水稻 ( Oryza sativa L.)产量和经济性的影响对于综合杂草管理至关重要。在这里，连续两年（2017-2018 年）进行了田间试验，以确定不同密度的阴道分枝杆菌（0、1、4、8、12、16、20和 24 株 m ^–2）对水稻的产量损失、经济门槛和总收益。结果表明，较高密度的阴道分枝杆菌对早稻和晚稻的株高、每株分蘖数和调整后的总收​​益表现出更大的抑制作用。对单株穗数、每穗饱满粒数和千粒重的抑制作用也很显着，尽管比在其他产量性状上观察到的要小。手动除草下的阴道分枝杆菌的经济阈值从 2.80 到 4.44 株 m ^–2不等，而在 2 年内使用除草剂的阈值水平介于 0.71 和 1.03 株 m ^–2之间。所有其他因素的平均值，随着阴道分枝杆菌密度从 0 增加到 24 株 m ^–2，调整后的总回报下降了 45.0%. 考虑到经济门槛和总收益，应防止稻田杂草管理不合理使用除草剂。该研究为减少化学除草剂的使用、节省杂草管理成本和保护农田生态系统环境提供了有用的数据。