Establishment of alfalfa by interseeding it with corn planted for silage can enhance crop productivity but weed management is a challenge to adoption of the practice. Although a simple and effective approach to weed management would be to apply a glyphosate-based herbicide, concerns about herbicide resistance and limitations in available alfalfa varieties exist. Field experiments were conducted to compare the efficacy and selectivity of PRE, POST, and PRE followed by POST herbicide programs to a glyphosate-only strategy when interseeding alfalfa with corn. Experiment 1 compared PRE applications of acetochlor, mesotrione, S-metalochlor, metribuzin, and flumetsulam. Results indicate that acetochlor and metribuzin, and S-metalochlor used at a rate of 1.1 kg ai ha−1 were the most effective and selective PRE herbicides 4 wk after treatment (WAT), but each resulted in greater overall weed cover than glyphosate by 8 WAT. Experiment 2 evaluated applications of bentazon, bromoxynil, 2,4-DB, and mesotrione at early and late POST times. Several herbicides used POST exhibited similar effectiveness and selectivity as glyphosate, including early applications of bromoxynil (0.14 kg ai ha−1) and 2,4-DB (0.84 or 1.68 kg ai ha−1), as well as late applications of bromoxynil (0.42 kg ai ha−1), 2,4-DB (0.84 kg ai ha−1), and mesotrione (0.05 or 0.11 kg ai ha−1). A third experiment compared applications of acetochlor PRE, bromoxynil POST, and a combination of acetochlor PRE with bromoxynil POST. All treatments were effective and safe for use in this interseeded system, although interseeded alfalfa provided 65% to 70% weed suppression in corn planted for silage without any herbicide. Herbicide treatments had no observable impacts on corn and alfalfa yields, so weed management was likely of limited economic importance. However, weed competitiveness can vary based on several different factors including weed species, density, and site-specific factors, and so further investigations under different environments and conditions are needed.

中文翻译：

---

苜蓿与玉米青贮饲料的预施和后施除草剂选择

通过将苜蓿与种植用于青贮饲料的玉米进行间种来建立苜蓿可以提高作物生产力，但杂草管理是采用这种做法的挑战。尽管一种简单有效的杂草管理方法是使用草甘膦除草剂，但仍存在对除草剂抗性和可用苜蓿品种限制的担忧。进行了田间试验，比较了在苜蓿与玉米间播时，PRE、POST 和 PRE 之后的 POST 除草剂程序与仅使用草甘膦策略的功效和选择性。实验 1 比较了乙草胺、甲基磺草酮、小号-金属草胺、metribuzin和flumetsulam。结果表明乙草胺和metribuzin，以及小号-金属草胺的用量为 1.1 kg ai ha-1是处理后 4 周 (WAT) 最有效和选择性的 PRE 除草剂，但每种除草剂的总杂草覆盖率都比草甘膦高 8 WAT。实验 2 评估了苯达松、溴苯腈、2,4-DB 和甲基磺草酮在 POST 早期和晚期的应用。POST 使用的几种除草剂表现出与草甘膦相似的有效性和选择性，包​​括早期应用溴苯腈 (0.14 kg ai ha-1) 和 2,4-DB (0.84 或 1.68 kg ai ha-1)，以及溴苯腈的后期应用 (0.42 kg ai ha-1), 2,4-DB (0.84 kg ai ha-1) 和甲基磺草酮 (0.05 或 0.11 kg ai ha-1）。第三个实验比较了乙草胺 PRE、溴苯腈 POST 以及乙草胺 PRE 与溴苯腈 POST 的组合的应用。尽管在没有任何除草剂的情况下，在种植用于青贮饲料的玉米中，间种苜蓿提供了 65% 至 70% 的杂草抑制率，但所有处理方法都可有效且安全地用于该种间系统。除草剂处理对玉米和苜蓿产量没有明显影响，因此杂草管理的经济重要性可能有限。然而，杂草竞争力可能因杂草种类、密度和场地特定因素等几个不同因素而异，因此需要在不同环境和条件下进行进一步研究。