Tenacity Herbicide Review: A Cool Season Lawn Testimonial

One of the hottest lawn care herbicide products over the past couple of years has certainly been the rising popularity of Tenacity herbicide. Luckily I was able to get my hands on some for my fall renovation before they temporarily ran out of stock.

Made by Syngenta, Tenacity contains the active ingredient, mesotrione. This unique ingredient can not only be used as both a pre- and post-emergent herbicide, but can also be used as an effective crabgrass killer while controlling more than 40 other grassy and broadleaf weeds without affecting the germination of new grass seeds. 

After heavy core aeration and dethatching in the fall of 2018, and overseeding at 7 lbs./1,000 sq. ft. of Jonathan Green Black Beauty Ultra and GCI’s Premium TTTF, my grass came up nice and green. So green that I won the Jonathan Green ‘Show Us Your Lawn Content‘ for July 2019. However, there was one big problem: Creeping Bentgrass.

The core aeration propagated the bentgrass that was hiding under the soil. During the peak season, it was hard to notice – especially by those driving by or even walking along the sidewalk. However, the closer I looked, the more and more bentgrass I noticed. 

So, in late August, I started my attack. This was a little late in the game, particularly for Massachusetts cool season lawn, but we had a big lawn party on August 18th, and I knew I didn’t want to roll the dice with the possibility of a temporarily bleached lawn.  

Before the nitty gritty, here’s a quick overview of some frequently asked questions about Tenacity herbicide:

Tenacity Herbicide Application Rates

Tenacity application rates a post emergent herbicide:

  • Use the syringe that comes with the bottle of Tenacity
  • Mix 1/2 teaspoon of Tenacity with 1 1/2 teaspoons of non-ionic surfactant (NIS) to 1 gallon of water to cover 1,000 sq ft.
  • Spread evenly across lawn. Repeat in 10-14 days
  • Use a blue dye (optional) to avoid overlapping and ensure even coverage

Tenacity application rates as a pre-emergent herbicide:

  • Use the syringe that comes with the bottle of Tenacity
  • Mix 1/2 teaspoon of Tenacity to 1 gallon of water to cover 1,000 sq ft.
  • Water in with 1/4″ of water within 1-2 days of application

Be sure to always read the label before applying Tenacity herbicide.

How to Apply Tenacity Herbicide

  • Use the proper measurements as previously stated above
  • Fill a backpack sprayer with half of the total water (e.g. if you’re covering 2,000 sq. ft., then first fill to 1 gallon)
  • Add Tenacity herbicide and NIS (if using as a post-emergent) and fill with remaining water
  • Ensure product is mixed well – consider using a paint mixer drill attachment

Lawn Phix Tenacity Experiment

Not only was I up against an August 18th lawn party, but I also had to plan around the new roof being installed on the house on September 9, 2019. This 2-3 week period is the absolute sweet spot for overseeding for cool season lawns so the plan was made:

Tenacity herbicide post emergent applications:

  • August 19th and August 27th at full application rates. This is not ideal. If I had the time, these would have been spaced out two-weeks apart
  • September 12th dethatching, scalping, and overseeding
  • Starter fertilizer, Milorganite, and Kelp4Less
  • Daily waterings, 1-3 times per day

Midway through my Tenacity herbicide experiment, I was paranoid. “What did I do to my lawn?!“, I said everyday. I even had multiple neighbors come by and ask, ‘What in the world happened? Your lawn used to be so green‘. I had an ultra white, bleached lawn that I didn’t know if it was going to recover or not. “I’m never using this over-priced, over-hyped garbage ever again!“, I said on many occasions. 

Check out the images and timestamps below.

But low and behold, cooler heads prevailed and Tenacity herbicide didn’t disappoint. In fact, my lawn looks better than ever. There is only one small patch of bentgrass remaining that I will dig up and repair in the spring. 

The only word of caution: reset your expectations. I knew overuse of Tenacity herbicide could cause temporary bleaching of good turf grass, but I wasn’t expecting it. I used it on a friend’s lawn which I ‘consult’ for and did not have any bleaching of his good turf. While he had a bunch of crabgrass (which it smoked in two applications) his healthy grass stayed lush and green. 

I went from a non-believer to someone who will absolutely keep this gem in my arsenal. Whether I need to tackle bentgrass again, or simply want to add some to my tank to be used as a pre-emergent when overseeding, Tenacity will always be stocked on my lawncare shelf. 

Frequently Asked Questions (FAQs)

How long does Tenacity Herbicide last for?

Tenacity will last approximately 30 days as a pre emergent. Be sure not to use a non-ionic surfactant (NIS) when used as a pre-emergent.

Can Tenacity Herbicide kill and control crabgrass?

Yes, Tenacity can kill crabgrass, generally with less than 4 tillers. Spread application over 10-14 days. This herbicide can also be mixed with some other post emergent herbicides such as SpeedZone. Be sure to read the label.

Tenacity can also be used as a pre-emergent. However the efficacy will wear off in about 30 days, making Prodiamine and Dimension better pre-emergent options in preventing crabgrass.

Can Tenacity kill and control bentgrass?

Yes. Depending on the size and severity of bentgrass in your lawn, two applications of Tenacity, approximately 10-14 apart, should eradicate creeping bentgrass.

What are the application rates of Tenacity?

Five to eight fluid ounces (5-8 oz.) of Tenacity herbicide will cover one full acre.
When used as a pre-emergent:
Mix 1/2 teaspoon of Tenacity to 1 gallon of water to cover 1,000 sq ft.
Water in with 1/4″ of water within 1-2 days of application.

When used as a post emergent:
Mix 1/2 teaspoon of Tenacity with 1 1/2 teaspoons of non-ionic surfactant to 1 gallon of water to cover 1,000 sq ft.
Spread evenly across lawn. Repeat in 10-14 days

2 thoughts on “Tenacity Herbicide Review: A Cool Season Lawn Testimonial”

  1. I’ve had great success with removing bentgrass with Tenacity, so much so that I made my only YouTube video of the process for others to see. I was thinking of using my Tenacity as post-emergent weed control. I was going to do a blanket spray on my lawn to just kill off anything existing or anything that is starting to emerge. I also ordered the new kelp4less green lawn mix. Do you think it would be fine to mix the kelp4less with Tenacity and do a blanket spray? Then I can kill two birds with one stone.

    • Hi Dan! Thanks for the comment. Your video, in fact, helped me pull the trigger in doing this to my lawn. Awesome content! I think you could mix them together if you were to use Tenacity as a pre-emergent. But if it’s a post emergent killer, then no – only because you need a Non-Ionic Surfactant (NIS) for this method. I’d probably to two separate apps in this case.


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