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Agronomy Day 2009

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Tour A

Technology to Turn the Tide

Aaron Hager
Aaron Hager
Assistant Professor of Weed Science
Department of Crop Sciences
217-333-4424
hager@illinois.edu

Do you consider yourself generally to be an optimist or pessimist?  Think back a few years to when glyphosate-resistant crops were in the earliest stages of commercialization and adoption: were you optimistic that the ability to apply glyphosate in-crop for weed control would spell the end for troublesome broadleaf and grass weed species?  Were you pessimistic that you would ever again need anything other than glyphosate for weed control in corn and soybean?  Many folks initially shared a common perception that it was unlikely another herbicide or herbicide-resistant technology would be needed once glyphosate and glyphosate-resistant crops became commercially available.

Now, fast-forward to the present era in which shifts in weed spectrums and biotypes have occurred across a large portion of Illinois acres.  Later-emerging weed species, such as annual morningglory, giant ragweed and hophornbeam copperleaf, have flourished with the concomitant decreased utilization of soil-residual herbicides.  Glyphosate-resistant biotypes of horseweed (a.k.a. marestail) often frustrate farmers who attempt to control them chemically prior to planting no-till soybean.  Frustration continues to build when farmers have to contend with glyphosate-resistant waterhemp after soybeans emerge.  These examples illustrate how the once widespread optimism pertaining to the “invincibility” of glyphosate has been tempered by the realities imposed by the biological diversity inherent in Illinois cropping systems.

New technologies have or will soon enter the marketplace that may provide solutions to some of today’s most prevalent weed management challenges.  Historically, new herbicide active ingredients with novel sites of action have been the predominant form new weed management advances have taken.  Indeed, a new herbicide active ingredient (saflufenacil) will become commercially available in 2010 that will help farmers better manage some of the challenges encountered when attempting to control glyphosate-resistant horseweed before planting no-till soybean.  However, not all future weed management technologies will be packaged in a plastic jug; many will come as seed in a paper bag.

Several new herbicide-resistant corn hybrids and soybean varieties are scheduled to be commercialized during the next few years.  While these new hybrids and varieties themselves won’t contribute much to managing challenging weed populations, the herbicide-resistance traits contained within these new crop offerings will allow for in-crop applications of herbicides not previously used due to crop sensitivity.  For example dicamba, an effective postemergence herbicide option for control of glyphosate-resistant waterhemp in corn, cannot be used in soybean.  The future commercialization of soybean varieties resistant to both glyphosate and dicamba will make possible the use of dicamba in these soybean varieties for control of glyphosate-resistant broadleaf weeds.

Glyphosate-resistant horseweed can be particularly challenging to control chemically prior to planting no-tillage soybean.Figure 1.  Glyphosate-resistant horseweed can be particularly challenging to control chemically prior to planting no-tillage soybean.
Glyphosate-resistant waterhemp will become more common across Illinois cropping acres.Figure 2.  Glyphosate-resistant waterhemp will become more common across Illinois cropping acres.
change and challenge