Tenacity (mesotrione) is used to kill bentgrass, clover, and other non-desirables. I get how an herbicide could selectively kill broadleaf weeds while leaving grasses alone, but how does it manage to kill bentgrass and poa annua while not harming other turf grasses?

  • 1
    This herbicide must be involved in shallow roots. Poa annua and creeping bent grass are VERY shallow rooted. Golf courses are amazing that they use WEED grasses for their golf courses. Primarily so they can mow SHORT SHORT SHORT. Most grasses will not tolerate being mowed any shorter than 3" (cool season species). They don't grow deep roots so the golf courses have to water all of the time. It is interesting that this is where most people get their ideas about maintenance of their own home lawns. Homes next to the golf course are unable to grow dark green uniform lawns...weed grasses!
    – stormy
    Commented Aug 9, 2016 at 21:46
  • 1
    I am not sure these answers apply to Tenacity. It is a different animal from what I understand. It comes from a Bottlebrush plant and does not kill, but rather prevents the grass from breaking down the byproducts of the photosynthesis process. I am not sure how that applies to this question, but...
    – Evil Elf
    Commented Aug 10, 2016 at 12:20
  • 1
    The answer ~might~ lie in which metabolic pathways each species utilizes. More information on that: majordifferences.com/2014/03/…
    – Brenn
    Commented Aug 12, 2016 at 14:12

2 Answers 2


That particular herbicide is known as a HPPD inhibitor. It works by blocking an enzyme in the plants. The plants normally break down a particular amino acid (tyrosine) and use the components to build other needed substances. I'm guessing that normal lawn grasses get their nutrition via a different method, so blocking that enzyme doesn't effect them.

Wikipedia article on HPPD inhibitors


I checked on this herbicide and it's main use is for pre-emergence of grass seeds. Guess it must work but lawns shouldn't get to the point where you are able to see the soil. Haven't read the details for target species but pre-emergent chemicals can leach (move to other areas and into the water table), inhibit growth of other seeds in the garden and hamper growth of annuals and other young plants and then end up in our water.

The best way to not need this chemical is to grow dense, thick grass. Minimum of 3" in height. Then sunlight is not able to reach grass seeds/weed grass seeds such as Poa annua. Poa annua is very light colored and seems to always have seeds. That grass is what many golf courses use as well as the bent grass. One bird eats a seed, poops it out on a nice green lawn other than the golf course crop, if that lawn is too short then that seed will germinate.

Do you live near a golf course? Extremely important to understand how to promote your grass and not promote these shallow rooted golf course weed grasses. Keep your lawn thick so no sun gets to the soil and odd weed seed.

The best way to encourage the lawn grasses you want and discourage the weed grasses is by watering. Water only when the lawn bed is dry! When you walk across the lawn, your footprints will still be visible. This is the best signal that your grass needs water. This trains our genetically predisposed cool season grasses for the North West with huge root systems to grow deeper in an effort to reach further into the soil profile for moisture. This makes your lawn drought tolerant. Any little drought (like a day or two of no water) shallow rooted grasses will die out quickly and have little chance for seeds to germinate. While your lawn is thriving on once per week watering.

Look up the MSDS sheets for this product and it will explain the chemical in far more detail. I am just trying to explain how NOT to have to use any chemicals while having the best lawn you could imagine. Chemicals are band aids. In the real world if lawns were at all natural we wouldn't have to even add fertilizer or water. If it comes down to using chemicals then something is wrong.

Mow no lower than 3". Fertilize when necessary and use extended release fertilizer. Bag your clippings. Mulching is a nice idea but still not doable. Sharp sharp blades. What do you do for watering, for any chemicals added, for pH (lime addition)? For clippings...anything you can add we will be able to get your practices correct so you won't have to put band aids on problems produced by maintenance practices...a healthy lawn will never need any chemicals ever except of course fertilizer, possibly lime. That is it. Anything else is just a band aid for problems that can be prevented. I read the Tenacity brochure and trust me it is made for the company's benefit. No one needs this product. Healthy lawn by basic healthy maintenance practice is POSSIBLE! Get a soil test while you are focused with your lawn. Cheap, call your nearest Cooperative Extension Service of your main University. Without a test, never add lime.

  • Although this is informative, it doesn't address the question.
    – That Idiot
    Commented Aug 10, 2016 at 11:19
  • Yes it does...I addressed the BANDAID's relevance but in gardening as well as in anything the best remedy is PREVENTION. No chemical is going to help, I don't care how...'natural' it is. I have been a licensed pesticide applicator for decades. They NEVER talk about brand names...they teach basics of botany, explain how to PREVENT ever having to use pesticides. If one gets the basics down they don't have to use pesticide. Decades...lets talk about 4 full decades of experience and I have never HAD to use pesticides. Sure I experimented with a few but I try to share how NOT to use bandaids.
    – stormy
    Commented Aug 10, 2016 at 21:09
  • And this product is brand new, NOT well tested. I found a few endorsements that did NOT make sense...as in how using it makes lawn wonderful...from the very beginning? Hello?
    – stormy
    Commented Aug 10, 2016 at 21:20
  • 1
    I disagree. The question does NOT ask about the BANDAID's relevance. It doesn't ask about the research or how long it has been in use. No part of the question asks about the morality of using the chemical, the effectiveness of the chemical vs other treatments, or even make mention of its listing as a reduced risk pesticide. Responses to this questions (and all questions on this stack exchange) should be limited to providing information that answers the question. Soap boxing, diatribes, and peripheral opinions or facts should stay in the comments.
    – That Idiot
    Commented Aug 11, 2016 at 11:54
  • Gee, I am sorry that I am opinionated? As Master Gardeners we are taught to discourage chemicals and teach how to prevent ever needing chemicals. I don't think that my 'style' is so bad, it is just me giving from MY experiences, knowledge, training, education...otherwise I feel going out and finding answers to questions on the internet and reiterating these OTHER opinions is...sigh...not my style. I guess I have an agenda. To help others understand that reaching for chemicals is not the only answer nor is it the best.
    – stormy
    Commented Aug 11, 2016 at 21:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.