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Concerns over Roundup Ready Creeping Bentgrass
by
Bob Hartzler

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Sept. 2, 2004 - A reader questioned my statement about 'creeping bentgrass not being invasive under any situation' (3rd paragraph).  In retrospect this probably was too strong of wording, but as an agronomist I tend to use the word 'invasive' to describe plants that move into 'non-managed landscapes' (prairies, wetlands, forests, etc.).  Creeping bentgrass can move into areas planted with other turf species, such as Kentucky bluegrass, perennial ryegrass, etc.  RR creeping bentgrass will possess this same ability, but it should be no more aggressive than conventional bentgrass varieties.  When RR creeping bentgrass does move into adjacent turf areas, the only difference for the landscape manager is that glyphosate no longer will be a control option.  Although glyphosate very well might be the most effective control option available, there are other control tactics that can provide effective control.

April 12, 2004 -  Monsanto and The Scotts Company have collaborated to develop creeping bentgrass varieties that possess the Roundup Ready gene.  This trait will allow the bentgrass to survive glyphosate (Roundup), providing a powerful weed control tool for golf courses where creeping bentgrass is the primary species used for golf greens in the northern U.S.  Many greens keepers and avid golfers are anxiously awaiting the registration of RR bentgrass since it will provide an effective management tool for Poa annua (annual bluegrass), the leading weed problem on golf greens.  Just as genetically modified crops have faced resistance from many groups, Roundup Ready creeping bentgrass is facing opposition by persons not wanting to see it registered for release.  A recent article in the Des Moines Register (April 10, 2004) addressed some of these issues. 

There are two major concerns with introducing a herbicide resistant gene into a non-food crop such as creeping bentgrass.  The first is that the herbicide resistance gene will enable the plant to spread unchecked into areas where it is not wanted.  The second is that the introduced gene, in this case the Roundup Ready gene, may move from creeping bentgrass to other species, therefore making them resistant to glyphosate.  The Des Moines Register article focused on the first issue, and featured a headline quoting a senior weed specialist with the U.S. Bureau of Land Management: "Our concern is that if it was to escape onto public land, we wouldn't know how to control it".

The weed specialist implied that the ability to survive glyphosate will make RR creeping bentgrass a formidable weed.  However, herbicide resistance by itself doesn't make a plant a successful weed.  To determine whether RR creeping bentgrass poses a threat as a weed, one must evaluate whether the species moves from areas where it is being grown into adjacent habitats.  I am not aware of creeping bentgrass being invasive in any situation, thus the introduction of the RR gene should not create a new weed problem.  If RR creeping bentgrass would move from an area where it has been planted to other sites, alternative control tactics (mechanical tactics and alternative herbicides such as clethodim, sethoxydim, etc.) are available to manage the plant.  Thus, I do not feel RR creeping bentgrass poses a significant threat as a new weed problem.

The other risk, movement of the RR trait into other species, can be evaluated by determining the frequency and weediness of close relatives of creeping bentgrass in areas where the new cultivars will be grown.  As part of the registration process this risk must be evaluated.  In Iowa, Agrostis alba (redtop) is the only common close relative to creeping bentgrass, and this species has limited weedy traits.  Thus, even if the RR trait moved to redtop it is unlikely it would provide the plant any ecological advantage that would contribute to it being a weed.

Herbicide resistance is a considerable problem in agriculture, and thus any technology that poses the threat of increasing the occurrence of herbicide resistant weeds should be carefully evaluated.  However, it is important to remember that simply being able to survive a herbicide does not make a plant a successful weed.  Roundup Ready soybeans are planted on over 7 million acres in Iowa annually, but I am unaware of a single problem associated with controlling RR soybean in adjacent habitats.  Since creeping bentgrass does not possess traits that favor its spread into adjacent habitats, introduction of the RR gene should not result in the species spreading from golf courses to other areas.

Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University

For more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
http://www.weeds.iastate.edu
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