2021年除草剂残留问题

作物 & 害虫的报告 - 04/29/21

The weather conditions from fall 2020 through spring of 2021 have been a completely different situation than on the same calendar dates a year ago.

The weather conditions from fall 2020 through spring of 2021 have been a completely different situation than on the same calendar dates a year ago. 干燥的秋天, 冬天, 春天的条件导致许多地区提前播种, as well as an increased concern in herbicide carryover from applications made in the spring and summer of 2020. Any discussion about herbicide carryover will focus on three key components: environmental conditions since herbicide application; chemistry of the applied herbicides; and interactions between the herbicide and soil conditions.

Our northern climate inherently places us at higher risk for carryover compared to other states to our south and east. Herbicides will break down more quickly in warm, 由于微生物和化学降解增加，土壤潮湿. 在整个夏季，我们通常会有温暖的土壤, but soil temperatures decline rapidly as we progress into the fall and herbicide breakdown will also slow down during this time. 重要的是要记住，除草剂在冻土中不会分解. 这对我们来说意味着大多数除草剂降解发生在夏季, 当我们有充足的降雨时，退化会更快. 只要天气干燥, herbicides can persist in the soil longer due to decreased microbial and chemical degradation. 在北达科他州的许多地区, 自2020年8月或9月以来，土壤状况肯定是干燥的, thus causing the concern for carryover.

除此之外，由于环境问题，还会增加结转的风险, there are certain soil properties that increase the chance of injury with some herbicides. 土壤pH值是除草剂降解的重要考虑因素. 这在该州的东部地区尤为重要, where high pH soils will reduce the breakdown of sulfonylurea and triazine herbicides. However, there is increased concern in areas of western North Dakota with pockets of low pH. 具体地说, the imidazolinone herbicides (imazethapyr, imazamox) will persist for longer in low pH soils (<6.0)，随着越来越多的土壤pH值较低的地区被识别出来，这将是另一个考虑因素.

One of the most important soil factors to consider for microbial breakdown of herbicides is the soil organic matter. In general, the higher the organic matter, the more microbial degradation will take place. 在北达科他西部有几个油田的有机质含量在2%或以下, 还有更多的农田，整个农田的有机物质含量低于2%. These soil types will also be at increased risk of carryover due to inherently less microbial activity. Fields with sandy knolls can also experience increased risk of carryover since those spots tend to be drier than the rest of the field.

Certain herbicides will also have an increased risk of persisting in the soil and causing injury in subsequent years. These are typically herbicides with a longer half-life, 1 / 2的化学物质降解需要多长时间.

虽然我们会使用许多半衰期相对较长的除草剂(如阿特拉津), fomesafen, imazethapyr, 和metsulfuron), 也许最常用的半衰期长的除草剂是氯吡酯, 在WideMatch中找到的, 限制, 以及类似的产品. Clopyralid has an average half-life of 40 days, 但在不同的土壤和环境中，这个时间从12天到70天不等. Clopyralid is also exclusively degraded by microbes. 所以在去年施用后几乎没有降雨的情况下, 在那些干燥的土壤中，微生物活动会减少. There is also an increased risk of clopyralid carryover in those soils with low organic matter or sandy knolls.

Most of the questions we have received this 冬天 on carryover have been about fields where clopyralid was applied in small grains and the plan is to rotate to field peas, 大豆, 或者2021年的向日葵. 这些作物都对氯吡酯敏感，每隔10次轮作一次.5 to 18 months, depending on product and rates used, following clopyralid applications. Since clopyralid is broken down by microbes, there are additional rainfall requirements that can decrease or increase the rotation restrictions. For instance, the WideMatch label specifically states “For rotation to field peas in 10.5 months, precipitation must be greater than 7.0英寸在10.乐虎集团WideMatch后5个月及以上.在6月1日至8月31日期间申请5英寸. 否则，建议在施用后18个月轮作大田豌豆。”. This label requirement is driven by the need for increased microbial breakdown that occurs in wet soils during the warm summer months. 本质上, we need most of the precipitation to occur during the summer months when we have these warmer soil temperatures.

那么，这对2021年种植这些敏感作物意味着什么呢. As with everything in agronomy, it all depends. If the rainfall requirements on the label were met, then it should be ok to plant these 作物 in 2021. Even though we have been dry over the last six months, most of the degradation occurred last summer, 许多地区在6月和7月有足够的降雨量来满足标签要求, even if the spigot turned off in August. 一些地区不符合规定的降雨量要求, and these locations will be at greater risk for carryover and crop injury if field peas, 大豆, 或者种植向日葵. One good resource to check for rainfall since application is your local NDAWN station. For example, the NDAWN station near Webster shows 5.2020年6月的降雨量为10英寸.2020年7月的降雨量为54英寸.73” in August of 2020, for a total of 9.在这段时间里. 所以如果在6月1日使用氯吡唑啉，那么降雨量就满足了要求. 尽管自2020年8月以来很少有水分, 水分是微生物降解的最佳时机.

Keep in mind that summer rainfall events can be variable and your fields may have received more or less rainfall than the nearest NDAWN station. 该州的一些地区没有收到所需的降雨, 种植一种更耐受性的作物将是最安全的补救措施. 豌豆之间, 大豆, 和向日葵, field peas will be the highest risk crop in some of these areas that barely met rainfall requirements. 大豆 和向日葵 might be ok in some situations, 但请记住，在大多数除草剂残留事件中, injury is more likely to occur in pockets, such as low organic matter or sandy knolls. One additional consideration is that clopyralid can also be released from degrading crop residue, so if there are piles of residue in areas of fields following some of our wind storms this spring, then injury may be observed there as well.

One final note specific to clopyralid. Many have called with questions about soil tests that report back clopyralid is present at a certain part per billion (ppb) or part per million (ppm) in the soil. 我花了一些时间调查了其他杂草科学家和一些行业代表, and the consensus is nobody has a clue what these numbers actually mean when it comes to risk of injury to sensitive 作物. So just because we can detect clopyralid in the soil doesn’t mean we have any confidence what those numbers actually mean for risk to a sensitive crop.

乔Ikley
扩展除草专家

This site is supported in part by the 作物 Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. 任何意见, 发现, 结论, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. 农业部.