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Is Tenacity (Mesotrione) Pre-Emergent Recommended?

by Allyn Hane 09 Aug 2023

What is Mesotrione?

Mesotrione is an active ingredient used to kill weeds both pre and post-emergent. If you have been anywhere on YouTube looking for lawn care tips on getting rid of weeds, you have seen videos talking about it. Probably what you have seen is the brand name, Tenacity. Tenacity is the brand name, Mesotrione is the active ingredient.

mesotrione

Nowadays, there are generics available that are much cheaper, such as this 8oz bottle of Meso 4SC. Do not buy it until you read this entire email because I’m going to tell you who should use it, when to use it, and what results to expect.

Mesotrione (Tenacity) For Warm-Season Turf

First and foremost, I want to stress that Mesotrione is mostly NOT for warm-season turf. If you read the label, you will see that the only warm-season turf listed is Centipede. St Augustine grass is also listed, but that is on sod farms only, not residential turf.



Even if it was labeled for St Augustine residential turf, there aren’t enough warm-season weeds that it controls to make it worth the investment. As a pre-emergent, it’s not too effective either. So don’t be tempted to waste money on this product, even if you see people in other groups breaking the label and using it on warm-season turf. The value isn’t there.

As mentioned, it is labeled for use in Centipede grass. In this case, its post-emergent properties in dealing with Crabgrass, Goosegrass, and Barnyardgrass can be useful. If you are dealing with any of those problem weedy grasses and you have Centipede grass, then Mesotrione is a good choice. If you have other weed problems over and above, there are much better alternatives.

As a pre-emergent, Mesotrione is only used at times of seeding. It is not a good pre-emergent for established lawns as it doesn’t last very long. It’s not a replacement for Prodiamine or Dithiopyr in your pre-emergent strategy.

Pre-Emergent – Mesotrione for Cool-Season Turf

For cool-season turf, Mesotrione is an effective tool, especially in the fall time when you may be thinking about seeding your lawn. That’s because Mesotrione is a pre-emergent herbicide that can be applied right alongside your grass seed and it will help to keep weeds from growing and competing with your seed but it will NOT harm your seed.

new seed & lawn restrictions

The key here is that you have to apply Mesotrione BEFORE your grass seed germinates. If you apply once it’s germinated and starting growing, Mesotrione will harm it. This is why I always recommend using Mesotrione as a pre-emergent with your seeding and to apply it on the same day as you seed, then water it in. Don’t wait.

mesotrione application instructions

Mesotrione will give you a good 3-4 weeks of pre-emergent protection which is plenty of time for your new grass to get growing and begin defending itself. Mesotrione is NOT a replacement for Prodiamine or Dithiopyr in established lawns. It doesn’t last long enough and will not perform as well in existing turf. Always keep in mind, the usefulness of Mesotrione as a pre-emergent is only in conjunction with seeding.

Post-Emergent – Mesotrione for Cool-Season Turf

Mesotrione is also an effective post-emergent weed control and if you purchased some because you needed it during your seeding project, then you probably have some leftover. If that is the case, then go ahead and use it up. It will kill lots of weeds that you face including dandelion and clover and is also good on weedy grasses like Crabgrass, Goosegrass, Creeping Bentgrass, Annual Bluegrass and
Barnyardgrass. It also does pretty well on Yellow Nutsedge.

Just remember, if you are going to use it AFTER you have seeded, you need to wait for 3-4 mowings or 30 days after germination.



I’ve always considered Mesotrione to be a “specialty herbicide” meaning, it’s used when you have identified a specific issue in the lawn that only Mesotrione can address. This goes back to those weedy grasses. If you specifically have issues with Creeping Bentgrass for example, then purchasing Mesotrione is a good idea.

However, if your primary weed problems come from broadleaf weeds like Creeping Charlie, Henbit, Spurge, and Plantain, then there are better, cheaper alternatives like Speed Zone which contains 4 active ingredients instead of just 1.

In other words, Mesotrione isn’t a “general purpose” weed control for the most part. It’s used in specialty situations such as when you are seeding or when you face a specific problem like Creeping Bentgrass. Outside of that, it’s best to choose something else and save the money.

I’ll be talking a lot more about this subject and many others relating to fall-time weed control, seeding, and pre-emergent. Subscribe to my podcast for even more detailed breakdowns over the coming weeks.

I’ll see you in the lawn!

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