# Bentgrass and Tenacity



## Riverman1 (Jul 4, 2020)

A year ago I had a lawn that was about 50% Bentgrass. In August I sprayed it with glyphosate (8000 sq ft) and reseeded it in early September with a mix of KBG and perennial ryegrass. The grass came up beautifully and looks great this summer. The problem is I am now seeing some small patches of Bentgrass returning. Some patches are palm sized and others as large as a basketball. My question is whether I should try to just spray the areas with tenacity where I can see it or spray the entire lawn? My concern is there is lots of small patches I can't see it. Also does anyone know the mix rate for perennial ryegrass per gallon? Thank you


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## bernstem (Jan 16, 2018)

Blanket spray the lawn at a low dose to highlight the Bentgrass without causing much bleaching of the Bluegrass and PRG, and then follow-up with spot spraying. Bent hides well in Bluegrass/PRG.


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## Riverman1 (Jul 4, 2020)

I like that idea. What would a "low dose" be per gallon?


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## SpiveyJr (Jun 7, 2018)

What about mixing in Triclopyr with the tenacity? People have mentioned it to help with the kill. Is that something that should be done with the blanket spray or with the follow up?


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## bernstem (Jan 16, 2018)

Dose per gallon depends on area applied to. I would target one gallon per 1000 square feet. A 2 Oz/Acre rate is a good starting point to highlight undesirables. 2 Oz/Acre is 0.27 tsp/1000 which is close enough to 0.25 tsp/1000 square feet to use 1/4 tsp.

Perennial Ryegrass is more sensitive to Tenacity than KBG so will bleach more with blanket sprays and the follow-up spot spraying. Do not apply Tenacity to Ryegrass at more than 5 Oz/Acre. Bentgrass may need more than one application of Tenacity to eliminate. The label recommends using a surfactant and up to three applications. Multiple applications at 4-5 Oz/Acre may thin your Ryegrass in those areas.

You can also use the Tenacity to highlight the Bentgrass and then hand pull as it will be easier to see.

I have no experience mixing Tenacity with Triclopyr, but there are several studies that recommend it for Bentgrass control. I would highlight with Tenacity alone and use the mix for the follow-up spraying.


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## SpiveyJr (Jun 7, 2018)

The thing with bentgrass is it hides so well in KBG and TTTF when first starting out. I was out this morning and noticed a few spots that stick out when there's dew on them, that I hand pulled, but when you start pulling there's really a lot more down low in between the good grass that you can't see. I feel like blanket spray is the only option.


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## Riverman1 (Jul 4, 2020)

At the .25 tsp/gal/1000 sq ft rate, do you think only the bent grass will bleach or will other grasses bleach too? I'm wondering because it may be difficult to single out the problem areas if both the BG and PRG are bleaching.


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## g-man (Jun 15, 2017)

Your location says "google". It makes it hard to give good advice to your weather.

Tenacity at 2oz/acre rate should not bleach your kbg. Mixing triclopyr helps limit the bleach of kbg.


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## ken-n-nancy (Jul 25, 2017)

Riverman1 said:


> A year ago I had a lawn that was about 50% Bentgrass. In August I sprayed it with glyphosate (8000 sq ft) and reseeded it in early September with a mix of KBG and perennial ryegrass. The grass came up beautifully and looks great this summer. The problem is I am now seeing some small patches of Bentgrass returning. Some patches are palm sized and others as large as a basketball. My question is whether I should try to just spray the areas with tenacity where I can see it or spray the entire lawn? My concern is there is lots of small patches I can't see it. Also does anyone know the mix rate for perennial ryegrass per gallon? Thank you


Riverman1, first off, I want to say that your renovated lawn looks nice, well done!

Secondly, I want to chime in that bernstem's advice is spot-on. Spraying the entire lawn via a blanket spray at a low dose will enable you to identify the bentgrass to determine if you want to continue further treatments to the entire lawn or by spot spraying.

Thirdly, the removal of bentgrass from a Kentucky Bluegrass (KBG) or Perennial Ryegrass (PRG) cool season lawn is one of the key features of Tenacity. Even since before Tenacity was approved for residential use, it has been marketed and studied almost first and foremost for its it unique capability of controlling bentgrass in cool season turf. Heck, the Syngenta product overview page for Tenacity still mentions bentgrass in the #1 key feature. Alas, as time has gone by, marketing has shuffled the target weeds to focus on more marketable culprits such as crabgrass, but the ability to control bentgrass is a major part of what initially brought it to market, particularly for controlling bentgrass from "escaping" from greens on golf courses.

At a rate of 2oz/acre (essentially the same as 0.25 tsp/1000sqft), bentgrass should be revealed in a cool season lawn without any damage to KBG or PRG. At that point, you can decide whether to continue with blanket sprays at a higher rate (I believe the label recommends 5oz/acre for bentgrass control) or whether to make the additional treatments to only the areas with significant bentgrass.

My experience is that three treatments of Tenacity at 5oz/acre at 10-14 day intervals will wipe out the bentgrass. Some temporary bleaching of KBG or PRG will take place, but they will fully recover by about 4 weeks after the final treatment. In my situation, the bentgrass was eliminated permanently.

As an aside, for application of a lawn chemical that requires care in dosage, it is wise to make sure you have calibrated your spraying technique so that you can apply at a known rate. It is good to practice spraying just water on your driveway so that you can spray such that 1 gallon covers an area of 1000sqft. I'd highly suggest learning to do this before spraying a lawn chemical that should be sprayed in a controlled dosage, such as Tenacity or Plant Growth Regulator (PGR).

Lastly, even if you do overapply Tenacity (within reason) the KBG will almost surely recover. Just wait it out. The worst whitening of KBG will be about 7-10 days after application. By 21-28 days after your last application, the KBG will be pretty much back to normal again, and any creeping bentgrass will be gone.

As a data point, a few years ago I tried to eliminate fine fescue from a northern mix by spraying Tenacity at 8oz/acre, with two doses 14 days apart. The experiment whitened the FF, PRG, and KBG, but as far as I can tell, it all recovered, making my experiment to eliminate the FF unsuccessful. I mention this to give you reassurance that even if you do get some bleaching of your desirable grass, it will recover. A photo of what two doses of 8oz/acre will do can be seen below (Tenacity was applied on the right, but not on the left), with more photos in the associated thread.


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## Riverman1 (Jul 4, 2020)

I really appreciate all the replies and recommendations. Waiting for the tenacity to arrive so I can get started.

BTW My location is in southeastern Washington.

Thanks again.


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## Riverman1 (Jul 4, 2020)

It's been a week since I did the blanket spray at .25 tsp per gallon per 1000 sq ft. I am seeing some bleaching but not as much as I would have expected. Some patches of bent are bleached on one side and not the other and I know all of it was treated. Im not sure if it hasn't been long enough to see bleaching yet or if the dosage wasn't high enough.

At this point trying to decide if I should go ahead with the .5 tsp per gallon rate on the spots where I can see some bleaching. The label says 2-3 treatments at 5 ounces per acre are needed to kill Bentgrass and to not exceed this amount on PRG.

Any Thoughts? recommendations?


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## g-man (Jun 15, 2017)

Do another app at the 3oz/a rate with nis. Tenacity is slow to show the effect. Like 10 day slow.


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## Riverman1 (Jul 4, 2020)

Thanks. Will the tenacity kill Bent at the 2 oz per acre rate I put down the first time?


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## g-man (Jun 15, 2017)

In one app, nope. You need multiple apps. Since you have prg, you need to walk the line between killing the bent without damaging the pgr too much. Or do round up and reseed. Prg grows so fast that it could be an option.


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## Riverman1 (Jul 4, 2020)

At the .25 tsp/gal/1000 I haven't seem any damage to the PRG. Zero. Some of the Bentgrass whitening (day 8) but other sections don't seem to be affected at all. Today I will spray again at a slightly higher dosage. Thank you for the help.


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## Babaganoosh (Apr 21, 2019)

Here is a great article about tenacity and creeping bent grass. You can go as low as 1oz rate and effectively kill the bentgrass.

https://www.golfdom.com/improve-the-efficacy-of-tenacity-for-creeping-bentgrass-control/


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## Riverman1 (Jul 4, 2020)

That's an interesting study, thanks. So far what I'm seeing at the 2 oz per acre rate is only part of the Bentgrass patch turns white and other parts seem unaffected.


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## Babaganoosh (Apr 21, 2019)

Riverman1 said:


> That's an interesting study, thanks. So far what I'm seeing at the 2 oz per acre rate is only part of the Bentgrass patch turns white and other parts seem unaffected.


The urea increases the uptake of the tenacity and makes it more effective. Apparently raking the dead and or dying out helps as well.

I'm going to apply at 1.5 ounce rate 3 times and use a NI surfactant and urea.


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## HoosierLawnGnome (Sep 28, 2017)

Also, bentgrass doesnt like prodiamine, but is ok with dithiopyr, so you may want to use the former if you aren't already


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## Babaganoosh (Apr 21, 2019)

HoosierLawnGnome said:


> Also, bentgrass doesnt like prodiamine, but is ok with dithiopyr, so you may want to use the former if you aren't already


Good to know. Especially since I've already got prodiamine. Thanks.


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## jperm47 (Jul 29, 2020)

I watched a YouTube video where the guy put down new seed after the 2nd Tenacity application and the new grass effectively grew in the place of Bentgrass as it was dying out. Seemed like that was a bad idea as I was under the impression it has to all be raked out and then soiled and re-seeded? Once my Bentgrass is dead from the 2nd app of Tenacity should I rake it out and then re-seed or seed right on top of the dead / dying Bentgrass?


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## Babaganoosh (Apr 21, 2019)

As long as up get good seed to soil contact either should be fine.


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## elgrow (Mar 30, 2020)

I didn't want to start a new thread since this seems to be a good source of knowledge on Tenacity & Bentgrass.

I am dealing with a couple patches of Bentgrass and Nimblewill in my yard and did my first blanket application yesterday at the 2oz/acre rate(.25tsp/1000) to try and highlight all of the nimblewill and bentgrass since they tend to tunnel lower and under my Tall Fescue.

I am planning to reapply at the 10 day mark and 20 day mark but I am not planning to do blanket applications for the whole yard again, only want to attack the areas that have been highlighted by the first blanket application. Would it be best to continue at the 2 oz rate or scale up to the 4 to 5 oz rate/acre?

Secondly how do I know that I am applying the appropriate amount to those areas if I am not covering a solid 1k area? Do I do the math on the areas I will be spraying and then fill up a smaller portion at the correct rate and then continue walking at my normal blanket application pace? Or do I fill up my 1 gallon container at a normal rate, do my typical walk/pace and just pour out the leftovers that dont get used?

Appreciate any and all help!


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## Babaganoosh (Apr 21, 2019)

The 2 oz rate is perfectly fine. You could even go as low as 1oz. An addition of urea nitrogen and raking the area helps to get all of it.


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## eqttrdr (Aug 9, 2020)

Same here.... trying to figure out how/when/often to use Tenacity to start taking care of a Bentgrass problem but also overseed with some CGI Cool Blue mix


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## jperm47 (Jul 29, 2020)

eqttrdr said:


> Same here.... trying to figure out how/when/often to use Tenacity to start taking care of a Bentgrass problem but also overseed with some CGI Cool Blue mix


I am in same boat as you. I applied Tenacity on Sunday to a large portion of my lawn which has been taken over by Bentgrass. I intend to apply a 2nd application about 2 weeks after so figure Sunday / Monday Aug 24th and then start seeding the large patches of (hopefully) dead bentgrass. I'll then dethatch mid September and do a proper overseeding, with GCI TTTF / *** mixture. I got a 100 pounds of it as my lawn is really thin and is in desperate need of repair


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## jcs43920 (Jun 3, 2019)

When I bought my house I had a bad infestation of bentgrass. I did a full renovation last year and still notice it popping up here and there. I talked to a couple golf course superintendents and they said to get rid of bentgrass you really have two options. Kill it with glyphosate and reseed with perennial rye to quickly fill it in, or devote a month out of the year to spraying with tenacity and dealing with the bleaching and reseeding.

You could also rip it up and reseed but that's not going to do anything long term.


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## elgrow (Mar 30, 2020)

jcs43920 said:


> When I bought my house I had a bad infestation of bentgrass. I did a full renovation last year and still notice it popping up here and there. I talked to a couple golf course superintendents and they said to get rid of bentgrass you really have two options. Kill it with glyphosate and reseed with perennial rye to quickly fill it in, or devote a month out of the year to spraying with tenacity and dealing with the bleaching and reseeding.
> 
> You could also rip it up and reseed but that's not going to do anything long term.


I'm going with the second option right now. First application was on sunday and planning on using the whole month and potentially early into September to kill it off before doing a heavy reseed/reno with GCI TTTF.

Was just patrolling the yard and have already started to notice some whitening on clover and crabgrass in the yard. Starting to see some spots on nutsedge and bentweed. Nimblewill hasn't shown anything yet. Will keep everyone updated/continue following this post for progress.


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## knightfan (Sep 22, 2020)

I applied 2 applications of Tenacity + NIS on my creeping bent grass August 20th and September 3rd at a rate of 5oz/acre. 
I then aerated and overseeded with a KBG/Rye mix. The new grass seed is coming in great and so is the creeping bent grass. It is coming back. I can always tell because of the morning dew. It has a different look to it.

After the first app it turned white for only a couple days and then brown. After the second app it was toasted. I thought for sure I got it all but I was wrong.

After reading MANY studies I think 4 applications is the best thing to do along with raking out the dead stuff in between apps and adding UREA to the tenacity mix.

This bentgrass is relentless. Its going to be a fight forever. My neighborhood is riddled with it.

I was going to nuke it all but after reading story after story of it coming back after a total reno, I just dont think its worth it. I will just fight it with tenacity and a rake. May the best man win..


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## elgrow (Mar 30, 2020)

So I ended up doing 3 applications at the 2oz/acre rate. Did not rake between apps 1 and 2, but raked pretty heavily before application number 3. The spots with Bentgrass came up incredibly easy, but there were still a few spots where it seemed like it was rooted in pretty well. I am not sure if that was just a deep root that was dieing and hadn't completely dried out or what.

Noticed a little bit more greening up prior to the 3rd application but I have to say since then I have not seen much if any active bentgrass.

I seeded back on 9/13 and put down an application at 6oz/acre, bringing me up to 12oz for the year. I still have 4oz left to play with for my annual allotment so I am debating about doing another 4oz for preem and then call it a day, or hang on to it for a potential low dose in the spring when it becomes active again, thinking 1 oz applications if thats the case.

Overall I was very impressed with tenacity on bentgrass, and I think some of the studies and other user experiences of going with lower application rates, multiple times surely seems to work.


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## knightfan (Sep 22, 2020)

I thought mine was dead also but after reseeding and watering it came back to life. Maybe hang onto that last 4oz for the spring time and like you said, hit it with a couple more low dose apps. Or maybe use it all up now while its down. Tough call.

What happens if you go over your yearly allotment?? Does anyone know?


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## ken-n-nancy (Jul 25, 2017)

knightfan said:


> What happens if you go over your yearly allotment [for Tenacity]?? Does anyone know?


Once you go over the allotment, you are breaking the law, very similar to driving down the road at 70mph in a 65mph zone. If law enforcement finds out, you can get prosecuted. If prosecuted, you may be convicted if there is sufficient evidence against you.

Even if you don't get caught driving 70mph in a 65mph zone, you are at increased risk of bad things happening -- getting in an accident and wrecking your car or getting killed.

Even if you don't get caught applying Tenacity at more than 16oz/acre per year, one is at increased risk of bad things happening -- the grass is under stress (from the herbicide) for longer, so there is increased risk of whatever bad things might happen to it while it is in the recovery from the Tenacity application.

Folks on this forum (and others) have called Syngenta customer service to try to find the answer to the "What happens if I apply more than 16oz of Tenacity per acre per year?" The customer service representatives are extremely helpful and friendly. They are also very careful to never give any advice which conflicts with the label directions -- for to do so would be giving advice to break the law.

Folks on this forum (and others) have also called Syngenta to ask about what to do after an accidental overapplication of Tenacity far in excess of 16oz/acre/year. The answer has always been to wait for the grass to recover. I have never heard of them being told that they should have their soil carried off to hazardous waste disposal, that they are in danger of having contaminated their groundwater, that they will be unable to reseed, or any other long-term adverse consequence. I have never heard such folks report ill effects from accidental overapplications of Tenacity.

If you are concerned about the environmental impact or human risk impact of a high dosage of mesotrione, I would note that the EPA studies I've read indicate extremely low risks to humans for short-term, intermediate-term, and long-term risks. If you work through the numbers on the MSDS, you will find that an average adult human can drink an entire 8oz bottle of Tenacity without ingesting a toxic dose. That is not true for most "common household cleaners" in your house. Experimental Use Permits of mesotrione on crops have included single application levels of up to 1.5 pounds/acre of active ingredient, which would not be granted if there were a significant associated environmental risk. (I would note that 1.5 pounds/acre of active ingredient is equivalent to 48oz/acre of Tenacity.)

But back to your original question...

In short, it's illegal to apply more than 16oz per acre per year of Tenacity to your lawn. For anybody here to advise you to apply more than that would be advising you to break the law. Accordingly, it's not likely that you'll receive knowledgeable written advice to do so. I know I'm not going to advise you to apply it contrary to the label.

Even if I were to speculate that higher application levels (which could be managed to keep from adversely affecting desirable turf) will not have any short-term, intermediate-term, or long-term adverse effects upon your groundwater, animals or people that come into contact with your lawn, or any adverse effects upon your soil, I wouldn't advise you to make such applications, as (1) that would be advising you to break the law, and (2) I don't really know what I'm talking about other than as a reader of published reports.


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## Jack_62 (Apr 25, 2020)

Very informative thread. I am from Ontario,Canada. Across the lake from Michigan's thumb, and was wondering when optimal timing for tenacity application for bent grass control would be. I am looking more so towards 2021, I think it is too late this year


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## dwaugh (Aug 25, 2020)

ken-n-nancy said:


> ]If you work through the numbers on the MSDS, you will find that an average adult human can drink an entire 8oz bottle of Tenacity without ingesting a toxic dose.


If you use the surfactant as a chaser, does that lower the LD50?


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## estcstm3 (Sep 3, 2019)

Where does somebody get the nis to mix?


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## Green (Dec 24, 2017)

I like Bernstem's approach if you have time. And interesting factoid from Hoosier lawn gnome.


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## Green (Dec 24, 2017)

estcstm3 said:


> Where does somebody get the nis to mix?


You can get it at a garden center, Tractor Supply, Hardware store, etc. Or online.


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## ken-n-nancy (Jul 25, 2017)

dwaugh said:


> ken-n-nancy said:
> 
> 
> > ]If you work through the numbers on the MSDS, you will find that an average adult human can drink an entire 8oz bottle of Tenacity without ingesting a toxic dose.
> ...


 Definitely.

The 80/20 non-ionic surfactant I use is in EPA toxicity category 2, with a signal word of "warning." Tenacity is in EPA toxicity category 4 (the category of least toxicity), with a manufacturer-chosen optional signal word of "caution."

Just as an interesting aside, household vinegar is in EPA toxicity category 3. Table salt is also in EPA toxicity category 3. Most laundry detergents are in EPA toxicity category 2, but some are in toxicity category 1 (the highest category). Household bleach is EPA toxicity category 1. Of course, we know that pouring bleach on your lawn will kill it...


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## knightfan (Sep 22, 2020)

Great info. Thanks. Any thoughts on getting rid of my bentgrass??


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## ken-n-nancy (Jul 25, 2017)

knightfan said:


> Great info. Thanks. Any thoughts on getting rid of my bentgrass??


Personally, I've only had bentgrass in my lawn once, and it was in two patches, with the larger of them being about a 3-4 foot diameter mostly circular patch.

Applying Tenacity to the patches, plus about 3' around the patches also (so for the 3-4' diameter patch, I treated about a 10' diameter circle) in multiple applications got rid of the problem. Unfortunately, my treatment of that was back in the days before I kept a detailed register of everything that I do to the lawn (I now keep track of everything -- mowing, applications of any product, plugging, etc.) so I don't have the details as to what I did. My vague recollection is that I made 3 applications of Tenacity at roughly 10-14 day intervals. I'm pretty sure I used the standard 4oz/acre rate, as I think that's the only rate I've ever used except for when attempting to eliminate fine fescue from a northern mix (when I used 8oz/acre).

From what I've read, bentgrass elimination is best with repeated applications, even at a low dosage.

Personally, I have never had much luck with overseeding or sowing new seed in bare patches. I've always had problems with either weedy grasses such as _Poa annua_ or _Poa trivialis_ coming up along with the new grass, or had problems with the "germination watering" causing the surrounding grass to be too wet and encountering disease from being too wet for too long. Accordingly, I'm not a fan of overseeding or seeding small patches and I don't do it anymore.

In the case when I got rid of the bentgrass patch, the smaller patch still had some intermingled good grass in it, so I let it fill back in. A year later, you couldn't tell it was ever there. For the larger patch, I sowed new seed. It looked good the next spring, but ended up having _Poa trivialis_ in it, too, so I ended having to kill it off again a year later when it got too painful for me to look at. I then used KBG plugs to "checkerboard" the area and waited about another year for it to fill in. It did well for a couple years after that, although I just killed off and am renovating that section of lawn this fall to go to all KBG in that area (it had previously been a northern mix.)

Now, with KBG, I don't reseed any patches but either wait for them to fill in or transplant in plugs from a good area of lawn using a Pro Plugger, so that I can maintain pre-emergent coverage pretty much all growing season, with the exception of marginal pre-emergent coverage during late July and early August. (I apply prodiamine at a 3-month rate at forsythia bloom which is typically around April 15th for me, then again around August 15th, and around September 15th.)


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## iceprix (3 mo ago)

Riverman1 said:


> A year ago I had a lawn that was about 50% Bentgrass. In August I sprayed it with glyphosate (8000 sq ft) and reseeded it in early September with a mix of KBG and perennial ryegrass. The grass came up beautifully and looks great this summer. The problem is I am now seeing some small patches of Bentgrass returning. Some patches are palm sized and others as large as a basketball. My question is whether I should try to just spray the areas with tenacity where I can see it or spray the entire lawn? My concern is there is lots of small patches I can't see it. Also does anyone know the mix rate for perennial ryegrass per gallon? Thank you





Riverman1 said:


> A year ago I had a lawn that was about 50% Bentgrass. In August I sprayed it with glyphosate (8000 sq ft) and reseeded it in early September with a mix of KBG and perennial ryegrass. The grass came up beautifully and looks great this summer. The problem is I am now seeing some small patches of Bentgrass returning. Some patches are palm sized and others as large as a basketball. My question is whether I should try to just spray the areas with tenacity where I can see it or spray the entire lawn? My concern is there is lots of small patches I can't see it. Also does anyone know the mix rate for perennial ryegrass per gallon? Thank you


One-half teaspoon per gallon


Riverman1 said:


> A year ago I had a lawn that was about 50% Bentgrass. In August I sprayed it with glyphosate (8000 sq ft) and reseeded it in early September with a mix of KBG and perennial ryegrass. The grass came up beautifully and looks great this summer. The problem is I am now seeing some small patches of Bentgrass returning. Some patches are palm sized and others as large as a basketball. My question is whether I should try to just spray the areas with tenacity where I can see it or spray the entire lawn? My concern is there is lots of small patches I can't see it. Also does anyone know the mix rate for perennial ryegrass per gallon? Thank you


Tenacity = half teaspoon per gallon of water. This is according to the syringe label that is supplied with Tenacity. Note, I have tried this dosage on a test spot on a lawn with a lot of bent grass and after 10 days I see no results
using a Scotts


Riverman1 said:


> A year ago I had a lawn that was about 50% Bentgrass. In August I sprayed it with glyphosate (8000 sq ft) and reseeded it in early September with a mix of KBG and perennial ryegrass. The grass came up beautifully and looks great this summer. The problem is I am now seeing some small patches of Bentgrass returning. Some patches are palm sized and others as large as a basketball. My question is whether I should try to just spray the areas with tenacity where I can see it or spray the entire lawn? My concern is there is lots of small patches I can't see it. Also does anyone know the mix rate for perennial ryegrass per gallon? Thank you
> 
> 
> [/QUOTE
> The Tenacity directions call for a half teaspoon per gallon of water as per the label on the syringe that is supplied with the herbicide. I used this amount using a Scotts, one gallon garden pump sprayer but after 10 days I saw no results. I will try again using a powered sprayer and will double the amount to one teaspoon per gallon.


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## Marzbar (Aug 2, 2020)

Is this bentgrass?


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