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Shawn Askew, PhD                                     

Associate Professor, Turfgrass Weed Specialist
Virginia Tech
While Shawn Askew, PhD, focuses his research at Virginia Tech on improving turfgrass, much of his work is with the state’s extension services. When he started working at Virginia Tech 10 years ago, seven out of the first 10 calls to his extension office were about nimblewill, a perennial grassy weed that is a big problem for cool-season grasses. He started testing every product he could get his hands on, and he said mesotrione (marketed as Tenacity® herbicide) was one of the first exciting products he discovered.  

“Other than mesotrione, there isn’t any selective herbicide registered to control nimblewill in lawns. In addition to that, it is the broadest spectrum, at-seeding herbicide. It will control more, different types of weeds than any other product, and can use it for on-label cool-season turf.” – Askew  

Askew started including Tenacity (mesotrione ) in most of his herbicide trials to learn its effects. Based on the 150 trials he’s completed, he has identified some “golden rules” to keep in mind when working with the product.  

Golden rule:  Repeat applications on mature weeds is critical

“When you’re targeting weeds with a post-emergence application, Tenacity’s killing power is through starvation. [Its mode of action disrupts photosynthesis.] And it takes time. The need for repeat application of the foliar spray is important, and I believe a three-week interval is the most effective. More than four weeks may not be as effective, and less than three weeks you start to increase the potential for turfgrass injury.”  - Askew  

Golden Rule: Single application for new seeding

Askew explains that when applying Tenacity at seeding, there may not be a need for repeat applications, as is the case when applying post-emergence. Development of target weed seedlings is much slower and can therefore be effectively controlled with a single application.  

“Tenacity is an excellent, very effective product for at-seeding applications and has a lot of benefits. You’ll control crabgrass, barnyardgrass, yellow foxtail and other annual grasses. You’ll also get more than half of the broadleaf weed species that are present on any given location because there are so many on the label.” - Askew 

Understanding the whitening effect on desirable turf

“The faster the leaves are growing on the plant, the more chance you’ll see white leaf tips because the leaves are probably being produced faster than the plant can metabolize mesotrione. That does not mean you are permanently harming the plant, and I believe any injury of the desirable turf is unlikely. Rest assured if it does happen, it is short-lived and will mow off in one to two mowings. Homeowners should just need a brief explanation of how the product works. Many may see it as positive, because they are going to see visual activity on the target weeds.” – Askew

©2011 Syngenta Crop Protection, LLC., 410 Swing Road, Greensboro, NC 27409. Important: Always read and follow label instructions before buying or using this product. The label contains important conditions of sale, including limitations of remedy and warranty. Tenacity® is not currently registered for use in all states. Please check with your state or local extension service prior to buying or using this product. Tenacity® and the Syngenta logo are registered trademarks of a Syngenta Group Company.

 




Bruce Branham, PhD                                              

Professor, Department of Crop Science
University of Illinois

Bruce Branham, PhD, has been researching weed control issues for the majority of his 28 years in academics, first at Michigan State University and now with University of Illinois. He has completed between 50 and 100 trials with mesotrione (marketed as Tenacity® herbicide) since the early 2000s.   

In central Illinois, nimblewill is a perennial grassy weed that no registered product could selectively control in turf. Branham’s research found that Tenacity offers excellent post-emergence activity on the weed.   

“Tenacity is an exciting product for lawn care; it addresses some issues that, in the past, we couldn’t touch. We just had to live with nimblewill, for example, but Tenacity can get rid of it. It can do things that no other herbicide can do. It has a lot of interesting weed control properties in turf.”  - Branham  

“Tenacity is interesting chemistry, and unlike other products on the market. It has very good post-emergence activity, but the real bonus is that it can be applied when you seed cool-season grasses such as Kentucky bluegrass. It will control most of the weeds you worry about but allow the bluegrass to come up. That’s unusual – other pre-emergence herbicides control the desirable species right along with the weeds. This property of Tenacity is very unique.” - Branham  

Many of Branham’s trials involved testing Tenacity rates and timing to control creeping bentgrass and annual bluegrass in Kentucky bluegrass.  

“If there is a contamination of creeping bentgrass in home lawns, there has been no way to get rid of it except using glyphosate and killing everything. Tenacity has the ability to control the weeds without damaging the desired Kentucky bluegrass” - Branham   

“As we do more work with Tenacity I believe we’ll find even more unique ways of controlling weeds that, in the past, we’ve just had to live with or kill the entire lawn and start over. Tenacity offers some real changes to how we think about weed control, it’s a unique chemistry and there may be even more to learn about it.” - Branham  

©2011 Syngenta Crop Protection, LLC., 410 Swing Road, Greensboro, NC 27409. Important: Always read and follow label instructions before buying or using this product. The label contains important conditions of sale, including limitations of remedy and warranty. Tenacity® is not currently registered for use in all states. Please check with your state or local extension service prior to buying or using this product. Tenacity® and the Syngenta logo are registered trademarks of a Syngenta Group Company.

 




Peter Dernoeden, PhD                                            

Professor of Turfgrass Sciences
University of Maryland

Plant pathologist Peter Dernoeden, PhD, has been with the University of Maryland for more than 30 years, where he serves as professor of turfgrass sciences. His work in weed control led him to start studying mesotrione (marketed as Tenacity® herbicide) more than six years ago. Dernoeden addressed three areas in the majority of his 20 trials with the product.   

1.    Evaluation of Tenacity for the selective removal of creeping bentgrass in tall fescue

Dernoeden spent more than two years in this area and found that three applications of Tenacity on a 21-day interval provided 95 percent creeping bentgrass control.  

2.    Assessment of Tenacity in spring seedbeds with different turfgrass species including tall fescue and perennial ryegrass

Dernoeden spent more than three years in this area and his studies showed that Tenacity can be used in spring seedbeds, as well as over top of seedlings of perennial ryegrass, Kentucky bluegrass and tall fescue. He found that two to three applications of Tenacity approximately 30 days apart provided very good pre-emergence control of crabgrass and several other weed species. This effective control resulted in improved establishment of the newly seeded areas.  

“Bottom line, Tenacity did a better job than the industry standard of promoting the establishment of these cool-season grasses because it controlled so many different weed species. It is incredibly unusual to have an herbicide that will control not only an annual grassy weed like crabgrass, but also sedges and broadleaf weeds. In our study, the competitive product only controlled crabgrass and foxtail. Spring seeding is an important area for this product.”  - Dernoeden  

3.    Assessment of post-emergence crabgrass control with Tenacity

“In the northeast, almost every lawn older than 5 years has both crabgrass and creeping bentgrass. The fact that you pick up at least two major weeds post-emergence with Tenacity is a big plus. It does take multiple applications, but the additional labor will be worth it for some lawn care operators.”  - Dernoeden  

More Study Results  

2008

Dernoeden and Jinmin Fu from the University of Maryland, and John Kaminski (then from the University of Connecticut), published findings of a Tenacity study in HortScience (2008;43(2):509-513). Part of the objective of the study was to evaluate the ability of Tenacity to selectively remove creeping bentgrass from Kentucky bluegrass and tall fescue. The field study was conducted in Connecticut and Maryland locations. The study determined that three summer applications of Tenacity provided the best combination of turfgrass safety and creeping bentgrass control.

2010

Dernoeden and University of Maryland colleagues C. P. Ryan and A. M. Adle determined the best rates of Tenacity for use in spring-seeding certain cool-season grasses in the paper titled “Tenacity® and Tupersan® for Weed Control In Spring Seeded Stands of Three Turf Species”. Tupersan (siduron) was chosen as the standard for comparison in this study.  

Although there were few significant differences among the Tenacity rates they tested, the data suggest two applications of Tenacity at 5 to 6 oz per acre would be optimal when targeting a variety of weed species in spring-seeded tall fescue and perennial ryegrass.  

The study also measured pre-summer cover ratings to determine the success of the herbicides to promote spring establishment. Weeds were so highly invasive that turf cover in the untreated control could not be assessed. Tenacity was more effective than Tupersan in promoting tall fescue establishment in the spring. Tall fescue cover increased from 50 percent to 95 percent between mid-May and mid-June in Tenacity-treated plots. Tall fescue cover in Tupersan-treated plots increased from 45 percent to 74 percent in the same timeframe. Tenacity was also more effective to Tupersan in promoting the early establishment of perennial ryegrass.

 

©2011 Syngenta Crop Protection, LLC., 410 Swing Road, Greensboro, NC 27409. Important: Always read and follow label instructions before buying or using this product. The label contains important conditions of sale, including limitations of remedy and warranty. Tenacity® is not currently registered for use in all states. Please check with your state or local extension service prior to buying or using this product. Tupersan® is a registered trademark of Gowan Company LLC. Tenacity® and the Syngenta logo are registered trademarks of a Syngenta Group Company.

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