RALEIGH, N.C. – With an estimated 1.3 million acres of cotton in the US mid-South taken over by glyphosate-resistant Palmer amaranth – commonly known as pigweed – growers are returning to tried-and-true integrated weed management programs in an effort to prevent costly damage.
“Achieving control before the weed reaches 1 to 2 inches tall is feasible, but once it gets beyond that, control measures can be costly, burdensome and many times less effective,” says James Whitehead, senior development technical lead for MANA Crop Protection in Oxford, Miss. “Experts are advising growers to approach every field proactively by using the right residual herbicide at the right timing to gain better results.”
由于抗草甘膦杂草现在已成为棉花生产的一个现实，蒙蒂塞洛阿肯色大学杂草推广科学家肯尼斯史密斯博士说，杂草管理的道路规则需要一种全新的方法。
“In cotton, we don’t have an over-the-top herbicide that will kill emerged Palmer amaranth, so we must go with residuals to keep them from germinating in Roundup Ready cotton,” says Smith. “In Arkansas, we’ve adopted the philosophy that glyphosate is now a tool for cleanup, not to kill the weeds.”
Studies show residual herbicides hold for an average of about three weeks, according to Smith, who recommends treating every two weeks – which signals a shift in strategy since the mid-2000s. “Back in 2004, we had almost gotten away from residual herbicides,” he says. “If we got the crop up, applied glyphosate with a residual herbicide, got a rain and it worked, great. We would come back with another treatment only if we had to. But that is no longer the case.”
Early-season use of residual herbicides – Smith recommends starting prior to planting – as part of an integrated systematic weed management strategy is critical to stopping glyphosate-resistant pigweed. Growers prevent not only early weeds, but can also address signs of or confirmed resistance.
After the crop emerges, he recommends growers follow up with an over-the-top treatment with metolachlor at the one- to two-leaf stage followed by another at the five- to six-leaf stage, and then scout closely at the 10- to12-leaf stage. “If weed seedlings are visible at the 10 leaf stage, a post-directed application of Cotton Pro® + MSMA is in order,” he says. “If the cotton is clean at the 10-leaf stage, we prepare to layby at the 12- to13-leaf stage with Direx + MSMA or Valor + MSMA.” Critical for success, he says, is rotating herbicides with different modes of action.
研究和农场经验表明，使用残留除草剂可以有效控制紫苋。最有效的控制是通过以系统方法重叠残留除草剂来实现的，该方法从种植前/出苗前时间开始，然后根据需要通过 layby 进行出苗后施用。在适当的时间使用具有多种作用方式的残留除草剂可提供额外的保护，并防止长苋菜在生长季定植。
While cultivation is a reliable technique to remove Palmer amaranth from young cotton, directed post-emergence applications can be successful after cotton reaches the six- to eight-leaf stage. “Careful scouting can target escapes in residual herbicides and allow needed time for effective post-directed treatment while the weeds are still young and have a height differential with the cotton,” Whitehead adds. “For layby, we’re seeing some growers use a post-directed application of residual herbicides to help remove small and late-germinating pigweed which helps to keep fields clean up until harvest.”
Smith 和 Whitehead 都认为，种植者永远不应依赖仅针对除草剂的抗性管理策略。一个全面的计划包括残留除草剂；轮换不同的行动模式；周围非农田的杂草控制；轮作;以及采用良好的耕作和耕作方法。
“Glyphosate-resistant weeds are expected to be an ongoing problem, but it’s a problem that farmers can manage,” says Whitehead. “It requires more management to avoid yield losses due to weed competition which means growers must pay more attention to product selection and timing.”
资料来源：MANA 作物保护；由总编辑 Jaclyn Sindrich 编辑