Halt multiple-mode herbicide resistant weeds

  • 01

    This glyphosate-resistant waterhemp in a central Iowa corn field is disturbing enough. It can get worse, though. An increasing number of waterhemp biotypes are exhibiting resistance to multiple herbicide modes of action.

  • 02

    When it comes to seed, terms like triple stack and quad stack are bantered about by farmers. That’s good. Unfortunately, the same triple and quad-stack terminology can be applied to weeds that resist multiple herbicide modes of action. That’s bad.

  • 03

    In 2011, Illinois weed scientists confirmed a quint-stack of resistance in the form of a waterhemp biotype that resists Glyphosate (Roundup), triazines (Atrazine), PPO inhibitors (Flexstar, Cobra), and ALS inhibitors (Pursuit). It’s expected this quad-stack will morph into a quad-stack this year or in 2013 when a waterhemp biotype that resists these four modes of action are joined by resistance to HPPD inhibitors (Balance Pro).

  • 04

    This resistance isn’t a knock against any of these chemical modes of action. Used properly, each of these herbicides and other corn and soybean herbicides play a vital role in managing weeds. However, it’s wise to mix up these action modes with multiple tactics, says Mike Owen, Iowa State University Extension weeds specialist.

  • 05

    Ever seen those 1980s retro commercials on late night TV that advertise everything from Ronald Reagan tribute videos to Madonna songs? If there was a retro 1980s commercial for farmers, you’d likely see a cultivator. This once-common weed management tool was obliterated when Roundup Ready technology debuted in the 1990s.

  • 06

    Cultivation will still be as rare as a good hair day for Donald Trump. Still, there may be some problem areas—such as spots with multi-mode weed resistance—where cultivation may be the best option. “The lion’s share of weed control will still be herbicides, says Owen. But adjust your management accordingly.”

  • 07

    Work done by the American agronomist C.E. Leighty way back in 1938 described crop rotation as “the most effective means yet devised for keeping land free of weeds.” That still holds true in 2012. And you don’t have to do it in strips either like in this picture. Good weed control lies in a variety of tools, including crop rotation, says Matt Liebman, an ISU agronomist.

  • 08

    Liebman notes back in the days before herbicides, farmers had to use tools like crop rotation and crop competition. “Crop competition is important,” says Liebman. “Avoid skips and address those areas that are drowned out.” Doing so will prevent weeds from gaining a foothold in thinly planted areas.

  • 09

    Lack of soil disturbance while planting also helps curb weeds. Doing so keeps weed seeds in the germination zone where they can be easily killed by herbicides. Tillage results in buried weed seeds that can surface years later.

Herbicide resistance isn't the end of the world. Here are a few ways to combat those weeds.

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