Don’t Skip Preemergence Herbicides in 2022 (05/12/22)
Spring 2022 has been about as polar opposite to spring 2021 as it can get in North Dakota. Last year, many no-till fields did not receive a burndown application due to the absence of weeds, and folks in the eastern part of the state were incorporating many preemergence herbicides due to concerns over adequate rainfall for herbicide activation. Weeds are back with a vengeance this spring. Winter annual weeds can be found in most fields, kochia has emerged and survived several blizzards and freeze events, and more summer annuals like green foxtail and waterhemp will soon join the fray. Of most concern to me, is this short planting window we now face. While there is great temptation to plant 24/7 whenever fields are finally fit, we need to be conscience of the fact that a preemergence residual herbicide is often the best tool we have for problematic weeds like kochia, waterhemp, foxtail, and wild oats.
We have noted increasing cases of herbicide resistance to the aforementioned weeds over the past several years. The latest confirmation is PPO-inhibitor (Group 14) resistant waterhemp in 7 counties in North Dakota. Kochia should be on the minds of most folks due to the challenges with kochia control in 2021. This article serves as a reminder that we should make sure to take the time and apply a preemergence herbicide in fields with a history of herbicide resistant weeds. In many areas, we have issues controlling foxtail (pigeongrass) and wild oats with postemergence herbicides in any crop that we cannot spray glyphosate postemergence. Waterhemp and kochia have become difficult to control in many crops, but especially broadleaf crops, including soybean. We have many premix and tank-mix options that can be applied preemergence or preplant incorporated to control these weeds in most crops grown in the state.
Of note for those who plant Xtend or Xtendflex soybean in order to use approved postemergence dicamba products, there is the looming June 30 cutoff date for those herbicides. Given the scrutiny these products face, I would not count on an extension of that cutoff date this growing season (though weirder things have happened). Preemergence herbicides will provide residual control of our problematic broadleaf herbicides, will delay the emergence and development of these weeds, and will delay the time it takes for weeds to grow to 4 inches, thus widening the window of application to effectively control these weeds with dicamba, or other postemergence herbicides. The last thing we want is for our backs to be against a hard cutoff date, or a challenging weather window to apply effective postemergence herbicides for weed control. Ensuring a preemergence program is applied is a vital first step to effective weed control in 2022.
Extension Weed Specialist