Dicamba-Resistant Pigweed? Troubling Signs Emerge – AgFax Weed Solutions

    Harrington seed destructor.

    Here is this month’s issue of AgFax Weed Solutions, sponsored by Nufarm’s Midwestern and Southern teams.
    Editor: Owen Taylor
    Web Editor: Ernst Undesser
    In Australia, new methods of weed control have evolved, and a group of American scientists toured the country’s ag production areas to see these systems in action. They came away with ideas about what might work now and which approaches deserve further evaluations.
    In a couple of states, researchers are seeing slippage when dicamba is applied to certain Palmer amaranth populations. These survivors turn up in tightly controlled comparisons, not random field observations. Consider these findings a wakeup call that is ringing very faintly at the moment – yet we can’t afford to ignore it.
    Of particular concern: kochia, giant ragweed, and marestail. Numerous populations of these species in Nebraska cannot be controlled by glyphosate because they have developed resistance to it. If you have had difficulty controlling these weeds in the last few years, make every effort to control them with an effective burndown application or tillage prior to planting.
    Eric Prostko, University Of Georgia Extension Weed Specialist, covers a wide range of topics relating to burndown and post-emerge options for 2020.
    As farmers and applicators head into the 2020 spray season, it’s time to brush up on the challenging realities of applying dicamba to Xtend crop fields. Here, we’ve rounded up the latest research and information you need to know before heading to the field with these herbicides.
    Palmer has gained more than a foothold in the state and could now make huge gains – particularly where the right herbicide programs aren’t implemented on 2019 prevented planting acreage.

    In certain fields in the state, Palmer pigweed has shown early indications of problematic control, says Extension Weed Specialist Larry Steckel. “(T)here is enough evidence for me to have informed those growers that dicamba will likely not provide consistent control of Palmer amaranth.”
    Nothing about this is foolproof but certain chemistries appear to have a better fit with cereal rye cover crops.
    Start your burndown planning by considering the likelihood that herbicide-resistant horseweed lurks in your field and seedbank. After another wet fall, a late harvest season and a mild winter, early weed management will be especially critical for anyone with horseweed in no-till production.

    Rainy spring conditions delayed burndown for most Tennessee producers. In this podcast, Dr. Larry Steckel, Extension Weed Specialist, discusses considerations for adapting burndown programs to later timing.
    “While it is difficult to estimate the precise role commercial bird feed plays, there is a distinct possibility it may be an overlooked pathway for spreading troublesome weed species.”
    First, here’s the good news: it appears that the new use pattern for dicamba in-crop has greatly reduced the horseweed seed bank in most fields. But there’s no free ride this year, especially with weather delays. Here are burndown options and strategies ahead of corn, cotton and soybeans.

    “I called the farmers and retailers who found some of these (Palmer pigweed escapes) and I told them, ‘Dicamba isn’t going to control Palmer amaranth in these fields anymore.’”
    For anyone who thinks new technology will handle all the weeds, perhaps an intervention is warranted – where the stubborn person is repeatedly thumped with a stick while being reminded of what happened the last time they opted out of residuals.
    Researchers in a multi-state project are trying to sort through all the variables that trigger temperature inversions. They find, among other things, that inversions often take shape during allowable application periods.


    AgFax Weed Solutions is published by AgFax Media LLC. If you’re receiving this newsletter from us, either a friend or business contact asked us to forward the report to you or you are a regular subscriber to one of our crop, pest and issue-related reports covering states in the Corn Belt, South, Southwest and Far West.

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    Questions? Contact Owen Taylor, 601-992-9488

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