Monday, February 13, 2006
Roundup Ready Corn Versus Roundup Ready Weeds
Yes, you are planting corn this year. And yes, you will have a weed control program. If Roundup Ready corn has been part of your operation, read on. If you are planting Roundup Ready corn for the first time, read on. If you have not decided, but are considering Roundup Ready corn, read on. If you want to refine your weed management program, with the use of Roundup Ready corn, read on. In other words, this perspective is about weed management and Roundup Ready corn.As you prepare your 2006 cropping and weed management plans, many farm operators will think that Roundup (glyphosate) is a magic bullet to cure their problems. Weed specialists Mark Loux, Bill Johnson, and Jeff Stachler at Ohio State University say, “Proper management of glyphosate and the Roundup Ready system is essential for growers to achieve consistently effective weed control and preserve maximum corn yield.”
One of the primary questions is: Do you apply Roundup once or twice? Fact: When allowed to grow to a size of 6 to 9 inches (grasses) or 16 inches (ragweed), these weeds cause up to 20% corn yield loss, due to their ability to compete with corn for nitrogen. In other words, you need to create a weed-free environment between 20 and 45 days after planting. So what are your options?
1) Glyphosate can be applied early enough to prevent competition between the weeds and crop, but a single application is unlikely to adequately control later-emerging weeds.
2) Because glyphosate is capable of controlling large weeds, it can be applied later in the growing season in order to control early and late-emerging weeds, but late applications will not adequately prevent the early-season competition between the weeds and crops that reduces yield.
The Ohio State recommendations say, “OSU and Purdue weed scientists generally advocate the use of residual herbicides (atrazine, Balance, Harness/Degree Xtra, Bicep II Magnum, Keystone, Guardsman Max, etc) in the Roundup Ready corn system to ensure the most effective weed control and minimize the risk of yield loss due to weed interference.” Their suggestion is to accomplish that with a pre-emergent application, followed by a post emergent application of glyphosate, or combine glyphosate with the residual herbicides in a post emergent treatment.
And you respond saying, that is a long list, with various costs; so which should I use? The weed specialists say, “Selection should really be based on the weed species diversity and density in each field. There are also programs available from several manufacturers that use incentives to promote use of the full labeled rate of their pre-emergence products. This can be an economical approach to Roundup Ready corn, when the incentives rebate growers some of the extra seed cost or the cost of the POST glyphosate application.”
On the flip side of the coin should be your concern about over-use of glyphosate. Does your county have a patch of marestail, waterhemp, or ragweed that glyphosate won’t touch? More and more weeds are evolving with glyphosate resistance, and researchers expect that to continue unless producers make good choices in their weed management system. Those choices should include:
1) Use tillage or burndown herbicides so that corn is planted into a weed-free seedbed.
2) For preplant burndown in no-till, do not rely exclusively on glyphosate, or use it in combination with 2,4-D or other herbicides that have activity on emerged weeds.
3) Do not rely on herbicide programs that consist of only postemergence herbicides.
4) In Roundup Ready corn, use rates of PRE herbicides that have significant activity on weeds species present in the field, and especially those weeds that are not always effectively controlled with glyphosate.
5) Make POST glyphosate applications when annual weeds are less than 4 inches tall (and when giant ragweed is less than 8 inches tall) to minimize their effect on crop yield and ensure more effective control. For larger weeds, apply at the highest labeled rate.
6) Make a second glyphosate application if weeds appear to be surviving an earlier application.
7) Application of glyphosate in combination with other POST herbicides may also slow the onset of herbicide resistance.
These issues can be considered “stewardship” of glyphosate. If you have concerns about the diminished impact of glyphosate to control certain weeds in your operation, the University of Wisconsin has a crop rotation key to designed with glyphosate management in mind.
If you are planting Roundup Ready corn, one of the requirements will be to buy and apply the correct formula of glyphosate. University of Illinois has a price comparison guide for glyphosate, as well as a formulation comparison guide for glyphosate.
Summary:
Your corn crop is like your kids, and to help them fend off schoolyard bullies, you need to manage weeds in your corn crop to avert a yield loss. With Roundup Ready corn, you have a new tool to help with weed control, but its use requires planning and management. Without proper management, your future cornfields will be full of schoolyard bullies that glyphosate could once control but no longer has the ability. With proper stewardship, weeds can be controlled, efficiently and effectively, in a Roundup Ready corn “management system.”
Apr. 13 Update:
Extension Weed specialists in the Cornbelt have begun publishing a new series of booklets, with specific directions for controling weeds that are becoming resistant to glyphosate.
Horseweeds
Wild buckwheat
(...and more are expected)
Posted by Stu Ellis on 02/13 at 07:00 AM | Permalink
Comments
Posted by: rachel at May 20, 2008 3:03PM
whats the impact of using roundup ready corn ?
Rachel:
Volumes could be written to answer your question, and I am unsure how detailed you want to get. The issues include greater expense than conventional seed, greater weed control potential, greater savings of time and labor, and a variety of others.
~Stu