How IPM can help with “superweeds”

Yesterday Paul Hollis from Southeast Farm Press wrote an eloquent and fact-filled blog about the myths behind “superweeds,” based on a new fact sheet published by the Weed Science Society of America. Mr. Hollis does an excellent job at explaining the points in the fact sheet, so you can read his article if you’d like to know how the “superweed” has become an average household word that, in fact, very few people understand.

Rather than debating the definition of a superweed, I’d like to explain how anyone–farmers and homeowners alike–can use integrated pest management to delay the onset of superweeds.

The term “superweed” came out following the wide adoption of herbicide-resistant crops, allowing the farmer to plant soybeans or corn or cotton and treat weeds around the crop without fear of killing the growing crop. I remember that many of the predictions included gene transfer between the GMO crop and some of the worst weeds, a prediction that seemed to be realized when stories about herbicide-resistant Palmer amaranth began to hit the news.

In 2010, I wrote two blog posts on superweeds, “Does Herbicide Use Encourage Superweeds?” (February 26) and “How to Resist Resistance” (May 14). Both tell the story about how a weed becomes resistant to herbicides when one class of herbicides is used too frequently.

Think about your own experience with medications. Suppose you take the same antibiotic every time you come down with an infection. Eventually that antibiotic stops working, and the doctor has to prescribe another antibiotic. Have you developed “supergerms”? No. The bacteria in your body has become resistant to the antibiotic.

The same principle applies to weeds. Glyphosate is among the cheapest of herbicides, so many people use it on their weeds (homeowners as well as farmers). All the time. Eventually, if you use that one herbicide enough times, the weed will develop resistance to it, just as the bacteria in your body develops resistance to one antibiotic.

So why not try a new herbicide? That’s just what many people did, so in several areas some weed species are resistant to multiple herbicides, and companies can’t develop alternatives fast enough to compensate for the losses.

That’s where IPM can help. In fact, weed scientists have adopted the term “integrated weed management” to refer to the rotation of weed management strategies, not just chemicals. Adam Davis, a weed scientist with USDA Agricultural Research Service, responds to a common myth about always being able to spray a way out of a weed problem:

“Over the past 60 years, weed scientists have been very successful in developing new herbicide chemistries to control weeds in a variety of crops and growing situations. But relying solely upon herbicides for weed management is not a panacea. First, the herbicide discovery “pipeline” is not inexhaustible. Herbicide registrations have declined substantially over the past 20 years due to regulatory constraints, the cost of product development and the genuine scarcity of novel chemistries. Second, less than 20 herbicide modes of action (the physiological mechanism by which an herbicide acts upon a plant) have been found, with the most recent discovery made almost two decades ago. Finally, excessive reliance upon a single mode of action can cause resistance and reduce herbicide effectiveness.

The widespread adoption of herbicide-resistant crop cultivars has intensified the problem, with cross-resistance and multiple resistance becoming more common. Successful long-term weed management will depend upon the adoption of integrated weed management practices that balance chemical, physical, biological and cultural control methods to preserve the usefulness of herbicides for generations to come.”

Before deciding on any type of control, you must identify the weed. Identifying a weed will help you decide whether a chemical will work, or whether it’s poisonous and dangerous to livestock. Knowing what weed you’re dealing with will also give you information about when and how it seeds, so you can control it before it has a chance to do any further damage.

Integrated weed management involves the use of several different types of tools, either together or at different times. For instance, mechanical methods such as mowing or hand-pulling is useful during early stages of weed development. Burning may be used after harvest if fire can be contained safely. Biological control involves insects, pathogens or possibly other plants that have a toxic affect on the weed (called allelopathy).

Sometimes wildlife such as goats are used to munch on weeds such as kudzu or poison ivy that have taken over an area. However, before you let the animals loose in an area, be sure that you know the weeds are not harmful to them.

Non-chemical tools are not meant to completely replace herbicides; they are actually used to help extend the life of the herbicide and delay herbicide resistance. Chemical tools still remain the cheapest, and excluding herbicide resistance, the most effective way of reducing weed competition in a field.

Some situations may sometimes require the use of non-chemical tools, however, including pastures if cattle will be grazing soon after the control is done. If weeds are poisonous to animals, they are a priority for removal.

In any case, the most important step is to first identify the weed. I can’t stress this point enough! When you’re dealing with multiple species of weeds and you have only so much time and money, knowing what weeds you’re dealing with helps you prioritize.

For more information about science-based information on herbicide-resistant weeds:

What is Integrated Weed Management? (Minnesota Department of Agriculture)

Weed myths (Weed Science Society of America, WSSA)

Herbicide resistance (WSSA)

Superweed fact sheet (WSSA)

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