No. 1 Article 5/March 25, 2011

Weeds 2011: What to Expect

Making (accurate) predictions about the types of challenges weeds might present during the 2011 growing season is a tenuous task. However, here at the outset of the season we will cautiously offer a few remarks about what weed management practitioners might encounter.

As mentioned in the "Product Updates" article in this issue, no new herbicide active ingredients are currently available in 2011. (There is a new active ingredient, pyroxasulfone, awaiting a label from the US EPA, but it might not arrive in time for use during the 2011 growing season.) Another way of stating this is that no new sites of herbicide action will be commercialized this season. We expect this situation to continue into the foreseeable future, which is likely to increase the challenges caused by herbicide-resistant weed biotypes and populations.

Last fall's corn harvest was much more timely and efficient than what many farmers experienced in 2009. One consequence of the challenging harvest of 2009 was the abundance of volunteer corn in 2010. Densities of volunteer corn were quite impressive, and careful attention was needed when selecting the appropriate control option. Volunteer corn will likely be a weed management consideration again in 2011, but volunteer corn densities are likely to be much lower than was experienced in 2010.

Our sense is that more acres of the 2011 soybean crop are scheduled to be treated with a soil-residual herbicide than were treated in 2010. Many challenges are posed by total postemergence weed control systems, including the unpredictability of being able to make timely postemergence herbicide applications before weed interference reduces crop yield potential. The high market prices for soybean, coupled with the increasing occurrence of herbicide-resistant weeds, suggest that soil-residual herbicides are likely to become staples of more integrated weed management systems. Keep in mind, however, that simply applying the herbicide to the soil doesn't guarantee optimal performance. In a future issue of the Bulletin we'll cover several factors that can influence the performance of soil-residual herbicides.

Herbicide-resistant weeds are poised to become an even larger weed management challenge in 2011. Results of recent surveys indicate that glyphosate- and PPO-resistant waterhemp populations are present in many Illinois counties and that glyphosate-resistant horseweed/marestail is very common across most of the southern third of the state. A waterhemp population from McLean County resistant to HPPD inhibitors was documented in 2010, increasing to five the number of herbicide site-of-action families to which Illinois waterhemp has evolved resistance. We expect that waterhemp biotypes resistant to multiple herbicide families will become even more common. There are also concerns with populations of giant ragweed and palmer amaranth in southern Illinois that have not been controlled by glyphosate.

These are by no means the entire waterfront of challenges weeds could impose during 2011, but they do represent issues expected to be widespread across much of the state. We'll do our best to keep you updated as more is learned about how best to manage these (and other) weed-related challenges in 2011.--Aaron Hager

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