# Growing Degree Days(GDD) and Trinexepac (Tnex) Applications



## SimonR

So most of us are on the Primo train and have been for a while. After speaking with MQ & Red a few times I think at times we have all observed how length of regulation is not always consistent. I think at one stage there was some talk of reduced effectiveness of the product the older it became. I know that from my experience in the past I have been caught out with some lack of regulation at times and inconsistent duration of suppression. I would look for signs of reduced suppression and re-apply based on that. Doing a quick bit of research on TLF the theory of Growing Degree Days (GDD) has been mentioned a few times.

Initially I was put on to the theory of GDD by a golf super here in Aus when I had my Greensmower serviced. The premise of GDD is that the duration of suppression is dictated by the air temperature. The rate has little to do with it. This growing season I have done a boat-load of research and found very few articles that cover-off Bermuda and other warm-season grass GDDs. Most GDD research has focused around bent-grass greens (C3 cool season). I then approached some agronomists in Aus and talked with them about how that translates to Bermuda (C4 warm-season) and what sort of accumulative GDDs should be adhered to. (about to talk degree Celsius here folks) Essentially what they were saying is that the accumulative effect on the C4 grass types is very similar, only C4 grasses don't really grow when there is an average temperature (24 hour period) below 10C. I finally found an article that supports this theory. 
https://turf.unl.edu/turfinfo/11-29_PGRUpdate.pdf

Once the 10C baseline is added to the GDD calculator, a 200GDD re-application for Primo becomes very similar for warm-season C4 grasses. So this season I have been using a modified GDD calculator for my Primo maxx applications and this is what I have observed.
Reapplication timing in days. 12, 20, 14, 14 (at 200GDD) at a rate of 8ml per 100m2 (sorry can't do that in fl,oz/ 1K) which is a much lower rate than i have used previously.
No over suppression or peaks and troughs in growth rates. It seems to be in optimum suppression all the time. No need to wait the 2-3 days for it to come back into suppression if you have waited a day or two too long for re-application. I can look at the forecast and if rain is due the day of re-application I can apply a day early and not worry about rebound.

I think we are all looking for that extra 2-3% with our efforts and this seems to work well. I would be interested in other members thoughts on the idea. I will upload my calculator once I can work out how!

Simon


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## Pete1313

Cool season member here, but I thought I would chime in as I have been following the work that Bill Kreuser has been doing with primo apps and GDD models and I too will be switching from a calender based application interval to a GDD based interval this season. As SimonR noted, application rate has more to do with intensity of suppression but not duration. Duration of suppression can be timed with GDD to avoid rebound. Bill Kreuser has made an online tool Greenkeeperapp that is free, and once setup will track your apps and GDD and tell you when to reapply. It also has all his latest research built right into the app. Anyone considering this approach should check it out. Not all grasses are the same. As SimonR said warm season grasses are calculated on GDD base 10°C, cool season is 0°C, but different species and how you maintain them can have an effect on the GDD app interval.

Examples-
A Kentucky Bluegrass field maintained at athletic field height on a fine textured native soil with an app rate of .250 oz/M will have a reapply target of 280 GDD base 0°C (504 GDD base 32°F)


Bentgrass maintained at putting green heights on a sand-based soil with an app rate of .125 oz/M will have a reapply target of 204 GDD base 0°C (367 GDD base 32°F)


Bermuda maintained at fairway height on a fine textured native soil and an app rate of .125 oz/M will have a reapply target of 225 GDD base 10°C (405 GDD base 50°F)




Bermuda maintained at a greens height on a sand based soil and an app rate of .125 oz/M will have a reapply target of 200 GDD base 10°C (360 GDD base 50°F)


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## osuturfman

Pete,

Using the GreenKeeper app, NICE!


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## Mightyquinn

SimonR said:


> So most of us are on the Primo train and have been for a while. After speaking with MQ & Red a few times I think at times we have all observed how length of regulation is not always consistent. I think at one stage there was some talk of reduced effectiveness of the product the older it became. I know that from my experience in the past I have been caught out with some lack of regulation at times and inconsistent duration of suppression. I would look for signs of reduced suppression and re-apply based on that. Doing a quick bit of research on TLF the theory of Growing Degree Days (GDD) has been mentioned a few times.
> 
> Initially I was put on to the theory of GDD by a golf super here in Aus when I had my Greensmower serviced. The premise of GDD is that the duration of suppression is dictated by the air temperature. The rate has little to do with it. This growing season I have done a boat-load of research and found very few articles that cover-off Bermuda and other warm-season grass GDDs. Most GDD research has focused around bent-grass greens (C3 cool season). I then approached some agronomists in Aus and talked with them about how that translates to Bermuda (C4 warm-season) and what sort of accumulative GDDs should be adhered to. (about to talk degree Celsius here folks) Essentially what they were saying is that the accumulative effect on the C4 grass types is very similar, only C4 grasses don't really grow when there is an average temperature (24 hour period) below 10C. I finally found an article that supports this theory.
> https://turf.unl.edu/turfinfo/11-29_PGRUpdate.pdf
> 
> Once the 10C baseline is added to the GDD calculator, a 200GDD re-application for Primo becomes very similar for warm-season C4 grasses. So this season I have been using a modified GDD calculator for my Primo maxx applications and this is what I have observed.
> Reapplication timing in days. 12, 20, 14, 14 (at 200GDD) at a rate of 8ml per 100m2 (sorry can't do that in fl,oz/ 1K) which is a much lower rate than i have used previously.
> No over suppression or peaks and troughs in growth rates. It seems to be in optimum suppression all the time. No need to wait the 2-3 days for it to come back into suppression if you have waited a day or two too long for re-application. I can look at the forecast and if rain is due the day of re-application I can apply a day early and not worry about rebound.
> 
> I think we are all looking for that extra 2-3% with our efforts and this seems to work well. I would be interested in other members thoughts on the idea. I will upload my calculator once I can work out how!
> 
> Simon


Great writeup Simon and very good info :thumbup: You are definitely giving me something to think about. How did you come up with the 8ml(.27oz) per 100m2(1076 sq/ft) application rate for your lawn? I am also going to be checking out that app and playing around with it this year too.


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## SimonR

Thank you Pete for the links to that app-site. It is amazing! I have spent most of the weekend adding in all my applications from the season and while it takes some getting to used to the detail it provides is fantastic.

MQ I just went with the rate that roughly matches my HOC as per the label. While I have a lower cut area i didn't want to be messing around with different application rates for different areas. Seems to give adequate suppression and with the GDD model no rebound at all


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## SimonR




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## Pete1313

Good to see you making good use of the app. I played around with it a bit last year, and it looks like they added some new stuff this year. I will use it more this season. Surprised it is a free app.


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## gijoe4500

How is "Lifespan" determined in relation to GDD? I've been playing around with the greenskeeperapp website, and it seems like it thinks 1 app of T-Nex will last for 4 months.


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## J_nick

gijoe4500 said:


> How is "Lifespan" determined in relation to GDD? I've been playing around with the greenskeeperapp website, and it seems like it thinks 1 app of T-Nex will last for 4 months.


I believe that's because you are experiencing lower temps so you're not accumulating very many GDD's per day. You've only accumulated 85 since 3/1/18, I don't think it forecasts future higher temps it rather goes off past data. Once you're getting 85 GDDs per week I think it will shorten the lifespan.


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## J_nick

@gijoe4500 do you have your location correct on the website? Make sure your pin on the map is in the correct spot.


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## gijoe4500

J_nick said:


> @gijoe4500 do you have your location correct on the website? Make sure your pin on the map is in the correct spot.


I do.


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## WarEagle26

Was looking into this a little bit today and noticed that Syngenta has GDD chart on their website that calculates based on the zipcode that you input.
http://www.greencastonline.com/growing-degree-days/home

Also, if you create a free account you can create different GDD thresholds (it appears you can add up to 5) and have notifications emailed to you when certain GDD thresholds are reached (email sent at 90% to give you a heads up and then at 100% when it is reached). You can even set it up so that it is recurring if you want to...it will zero out your GDDs when a threshold is reached and begin accumulating again and notify you when the threshold is reached again. This seems like it would be good to set up when you spray your first PGR app and then have it send you a notification whenever you need to re-apply.
http://www.greencastonline.com/growing-degree-days/home


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## J_nick

WarEagle26 said:


> Was looking into this a little bit today and noticed that Syngenta has GDD chart on their website that calculates based on the zipcode that you input.
> http://www.greencastonline.com/growing-degree-days/home
> 
> Also, if you create a free account you can create different GDD thresholds (it appears you can add up to 5) and have notifications emailed to you when certain GDD thresholds are reached (email sent at 90% to give you a heads up and then at 100% when it is reached). You can even set it up so that it is recurring if you want to...it will zero out your GDDs when a threshold is reached and begin accumulating again and notify you when the threshold is reached again. This seems like it would be good to set up when you spray your first PGR app and then have it send you a notification whenever you need to re-apply.
> http://www.greencastonline.com/growing-degree-days/home


I believe greencast uses GDD's in °F and greenkeeperapp uses GDD's in °C, you can't mix and match the numbers.

The conversion is 9 GDD's °F = 5 GDD's °C. So the picture @gijoe4500 posted earlier was from the greenkeeperapp where it's calculating PGR should be reapplied every 255 GDD's °C for his soil or 459 GDD's °F if you wanted to track it on greencast.

Tagging @Pete1313 as he's messed around with it more than I have.


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## Mightyquinn

J_nick said:


> WarEagle26 said:
> 
> 
> 
> Was looking into this a little bit today and noticed that Syngenta has GDD chart on their website that calculates based on the zipcode that you input.
> http://www.greencastonline.com/growing-degree-days/home
> 
> Also, if you create a free account you can create different GDD thresholds (it appears you can add up to 5) and have notifications emailed to you when certain GDD thresholds are reached (email sent at 90% to give you a heads up and then at 100% when it is reached). You can even set it up so that it is recurring if you want to...it will zero out your GDDs when a threshold is reached and begin accumulating again and notify you when the threshold is reached again. This seems like it would be good to set up when you spray your first PGR app and then have it send you a notification whenever you need to re-apply.
> http://www.greencastonline.com/growing-degree-days/home
> 
> 
> 
> I believe greencast uses GDD's in °F and greenkeeperapp uses GDD's in °C, you can't mix and match the numbers.
> 
> The conversion is 9 GDD's °F = 5 GDD's °C. So the picture @gijoe4500 posted earlier was from the greenkeeperapp where it's calculating PGR should be reapplied every 255 GDD's °C for his soil or 459 GDD's °F if you wanted to track it on greencast.
> 
> Tagging @Pete1313 as he's messed around with it more than I have.
Click to expand...

This is something I'm going to keep an eye on this year to compare the two websites to see if that math adds up as the whole °F-°C conversion has me a little perplexed and trying to find the exact GDD for bermuda and PGR seems a little fuzzy right now. I am liking where this is heading as it seems to be a more exact and precise way of applying PGR especially during the heat of summer when the window is actually shorter than 3 weeks.


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## Pete1313

The conversion from the number of GDD base 10°C to °F is what @J_nick said, basically multiply by (9/5). Just make sure you change the base temp to 50°F when converting.

I played around with the greenskeeper app alittle, but in the end I just took the GDD numbers and made my own spreadsheet.


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## ABC123

Pete1313 said:


> The conversion from the number of GDD base 10°C to °F is what @J_nick said, basically multiply by (9/5). Just make sure you change the base temp to 50°F when converting.
> 
> I played around with the greenskeeper app alittle, but in the end I just took the GDD numbers and made my own spreadsheet.


would you apply it every 280GDD or is that when it's lost it's effiecency and no longer controlling?


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## Pete1313

ABC123 said:


> Pete1313 said:
> 
> 
> 
> The conversion from the number of GDD base 10°C to °F is what @J_nick said, basically multiply by (9/5). Just make sure you change the base temp to 50°F when converting.
> 
> I played around with the greenskeeper app alittle, but in the end I just took the GDD numbers and made my own spreadsheet.
> 
> 
> 
> would you apply it every 280GDD or is that when it's lost it's effiecency and no longer controlling?
Click to expand...

For KBG at the .25oz/M rate you would reapply at 280 GDD base 0°C interval to avoid the rebound.


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## kur1j

Where do you get the number of GDDs before it isn't effective (e.g. how did you come to the basis 280GDD base 0*C?).

Also, if you want, just pull the GDD from wunderground.com. Here is an example in my area I did from April 1st to April 14th. I've had a total of 102 GDD.

https://www.wunderground.com/history/airport/KHUA/2018/4/1/CustomHistory.html?dayend=14&monthend=4&yearend=2018&req_city=&req_state=&req_statename=&reqdb.zip=&reqdb.magic=&reqdb.wmo=


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## Pete1313

kur1j said:


> Where do you get the number of GDDs before it isn't effective (e.g. how did you come to the basis 280GDD base 0*C?)


280GDD base 0°C is for Kentucky bluegrass only with a primo app rate of .250 oz/M. Warm season grass will be different and uses a base 10°C. Also different app rates of Primo will be slightly more or less GDD. The numbers are taken from the greenskeeper app(built into the app) and is research from Bill Kreuser from UNL.


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## kur1j

@Pete1313 Where did those recommendations come from? I'm not seeing anything in the Primo label.

Is there a site that just has a simple breakdown of "bermuda - application rate and number of GDD?"

So for example Primo max label shows .38oz/1k for Tifway 419. What would be the GDD for that rate? I'm also assuming that reducing the rate would also changed the number of GDD. So if i went up to .5oz/1k it would slightly increase the GDD? But how would i find or calculate that GDD?


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## Mightyquinn

kur1j said:


> @Pete1313 Where did those recommendations come from? I'm not seeing anything in the Primo label.
> 
> Is there a site that just has a simple breakdown of "bermuda - application rate and number of GDD?"
> 
> So for example Primo max label shows .38oz/1k for Tifway 419. What would be the GDD for that rate? I'm also assuming that reducing the rate would also changed the number of GDD. So if i went up to .5oz/1k it would slightly increase the GDD? But how would i find or calculate that GDD?


The whole GDD model is NOT going to be on the label. It is research that was done by a professor at U of Nebraska I think and has been replicated at other universities. The guy that came up with this has created the Greenskeeper app that you can create for your own lawn and put in your applications from there. When using a PGR, applying more AI may not always increase your length of control as the grass can only absorb so much of it. The lower you cut your lawn the less product you will need to apply as there is less leaf tissue for the plant to absorb. It's a fairly new method for ALL of us here and I think this will be the first year most of us will be using it, so it's a little bit of trial and error but the goal is to always have your turf in a state of control as the weather can have an effect on how long that is.


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## kur1j

@Mightyquinn

So I noticed on the website it cost? I put in all my information and it doesn't show anything regarding GDD. I added my "course" my sprayer, etc. Then go to add an application and don't see anything about GDD.


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## Pete1313

Did you set up your area(s) as well when you set up your "course"? After that, go to products and add primo maxx from the "+new public product" list.

Then go to new app, put in your sprayer and area of application and hit save.


Once that is done, below it will show you available products. Select primo maxx and then add to app.


Then below that it will allow you to enter your application rate. Input that and then the app will give you the default GDD based on your grass species and rate amount. That default number is based on the latest university research on GDD and primo maxx. For cool season grass, the GDD is a base 0°C. For warm season grass it is a base 10°C. 
(Note that this picture is the GDD number for Kentucky Bluegrass)


Here is some other info from Bill Kreuser on GDD
https://turf.unl.edu/turfinfo/9-28_GDD_Calcs.pdf

https://turf.unl.edu/turfinfo/11-29_PGRUpdate.pdf


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## Tellycoleman

Do the any of the apps provide GDD for Legacy?
I plan on rolling my own generic Legacy with Tnex and Paclo for part of my yard to compare it to TNex only. Sounds like both of those are better apps than what I was planning on using.


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## J_nick

Tellycoleman said:


> Do the any of the apps provide GDD for Legacy?
> I plan on rolling my own generic Legacy with Tnex and Paclo for part of my yard to compare it to TNex only. Sounds like both of those are better apps than what I was planning on using.


I just entered in Legacy on the greenkeeperapp and it put in 225 GDD's


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## Pete1313

Tide paclo is the app too.


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## J_nick

Pete1313 said:


> Tide paclo is the app too.


Aw, I just looked for Paclo and didn't see it. Brb


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## J_nick

Tide paclo was at 300 GDD's


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## Colonel K0rn

I'm reading through this, and setting up my products and I plan to use the T-NEX 1AQ, even though it has 11.3% AI, compared to the 12% that was purchased for the group buy. It's set at 225 GDD's for my soil type. A test entry for application on 4/9/18 at a rate of 0.25 oz/M has me at 21% suppression with a reapplication date of 5/25, but that's if our weather doesn't get much more crazy than it is.

I find myself having to juggle through the conversions of some of the oz > gr measurements when it comes to products like Celsius, as I measure those on a smaller scale. It always helps to double check the math, but it's nice when it's spelled out for you, like the PGR applications for a full and partial tank.


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## g-man

I think we should move this thread to the general section.

I like the app but it is not intuitive. The area that I wish they provide more guidance is the grass selection. What is the difference between roughs and athletic field to the app? The manual does not explain it.


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## Ware

g-man said:


> I think we should move this thread to the general section...


Agree. Done. :thumbsup:


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## Mightyquinn

g-man said:


> I like the app but it is not intuitive. The area that I wish they provide more guidance is the grass selection. What is the difference between roughs and athletic field to the app? The manual does not explain it.


I think those are in reference to your HOC as the PGR applications will be different and your length of control.


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## g-man

I know that hoc and soil affect the level of control. When I played with the app, changing the rate or the grass type(hoc) had an effect in GDD threshold. I'm planning on keeping 1in, so do I pick rough or athletic field? If I drop to 0.75in, then switch it to fairway?

Based on all the published papers and documents I've read, rate = % of supression but no real effect to GDD. GDD is affected by hoc and grass type. I've also read that too frequent could be a problem, but I haven't found a chart for GDD target as a function of hoc/grass type.


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## g-man

This grass selection bother me enough that I recorded each GDD value the app yields as a function of T Nex rate/grass selection. It was interesting.

These values applies to Native Soil - Fine Textured, for Mixed Cool season and for KBG too.

Rate	Green	Tee	Fairway	Rough	Athletic Field
0.125	204 261 261 261 261
0.25 204 280 280 280 280
0.5 204 317 317 317 317
0.75 204 353 353 353 353
1 204 389 389 389 389

So pick a rate and that's your GDD, the grass HOC doesn't matter to the app.

Edit: I tried to make this a pretty table. It looks pretty in when I edit, but not when I post.


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## kur1j

@Pete1313 Thanks! I see it now. I was selecting it from "custom product" instead of public product and it wasn't giving me the option.


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## kur1j

@g-man

How are you getting the default gdd to change with different rates? I've tried changing in various ways (saving, and deleting etc) and it never changes for me.


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## Pete1313

kur1j said:


> @g-man
> 
> How are you getting the default gdd to change with different rates? I've tried changing in various ways (saving, and deleting etc) and it never changes for me.


Might be different for warm season grass. His numbers are for Kentucky Bluegrass.


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## g-man

Look at the "greens" that it has the same GDD regardless of rate. It might be different for warm season grasses.


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## kur1j

I went and tried to get the same numbers he got and wasn't able to. I set it to KB, native soil. I was able to get the greens number of 204 with KB but even at .125 for KB i get 225GDD not 261.

Edit: Nevermine got it corrected to say 261 and can confirm for KB as the rate changes the GDD goes up. When I do the same thing for bermuda it doesn't change at all except from greens to everything else (200gdd vs 225gdd for everything else).

Just to make sure these are all GDD in C?


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## g-man

I just repeated it with KB, Fine Texture and I still get 261.


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## g-man

GDD 0C It is way easier to subtract 0 from the mean temp, than subtract 32 for GDD 32F.


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## J_nick

kur1j said:


> Just to make sure these are all GDD in C?


Yes, greenkeeperapp.com uses GDD in °C


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## kur1j

g-man said:


> GDD 0C It is way easier to subtract 0 from the mean temp, than subtract 32 for GDD 32F.


But for us warm season guys baseline is 10C or 50F :-D. So get the average temperature and subtract 50. So for cold weather grasses easier in C warm season grasses easier in F, at least for me. No matter though, looks like i'm getting a big fat 0 for my GDD today no matter what. High of like 54F :-/.


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## kur1j

@g-man

Yeah you are correct. Your numbers are right.

My observation is that with bermuda no matter the application rate the GDD doesn't go up. The only thing to affect the gdd is the green vs other HoC.

Rate, Est. HoC, GDD
.125 rough 255gdd
1.0 rough 255gdd

.125 tee 255gdd
1.0 tee 255gdd

.125 green 200gdd
1.0 green 200gdd

Everything for bermuda is 255GDD other than greens which is 200gdd.


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## Ral1121

kur1j said:


> @g-man
> 
> Yeah you are correct. Your numbers are right.
> 
> My observation is that with bermuda no matter the application rate the GDD doesn't go up. The only thing to affect the gdd is the green vs other HoC.
> 
> Rate, Est. HoC, GDD
> .125 rough 255gdd
> 1.0 rough 255gdd
> 
> .125 tee 255gdd
> 1.0 tee 255gdd
> 
> .125 green 200gdd
> 1.0 green 200gdd
> 
> Everything for bermuda is 255GDD other than greens which is 200gdd.


Those gdd are in °c so I have to convert them to °f correct?


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## g-man

Yes, these are GDD base 0C


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## kur1j

GDDc = 5/9 * GDDf

GDDf = 9/5 * GDDc

To calculate GDD:

Warm Season Grasses

GDDf = max((Tf_high + Tf_low)/2 - 50f , 0)
GDDc = max((Tc_high + Tc_low)/2 - 10c, 0)

For cool season grasses 50f is 32 and 10c is 0.


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## g-man

^+1


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## Ral1121

Thanks,. I am using the spreadsheet that was linked in another thread. Shows I will only end up with around 22 days before I have to reapply. I wish I would have bought more pgr


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## g-man

I did not enjoy using the greenkeeper website. I wanted more info to help plan. Therefore I used the charts/script that TurfHacker developed and modified them. I then also used a PACE excel files for soils and MLSN and modified it too. I placed it all into my google sheet log.

Blue pill - keep using the greenkeeper website.

Red pill - I'm sharing my spreadsheet. Make a copy and edit it to make it work for you. You will need to get your own Weather Underground API key (free). You will then need to setup the info in the setup tab. Ensure you pick a WU weather station near your house. Then you will need to run the script and make sure it all works. Finally, setup the script to run once a day *only* (4am), multiple entries of the same day screws this up.

What you get? Weather info from the previous day plus weather forecast will be used to graph the growth potential, sum the GDD 0C, ETo, Dollar Spot risk, Temp chart, etc. The charts plot the past and forecast in different colors.

You could also setup the Climate tab with the weather almanac info so it calculates your historical GP by month. This then also calculates the potential usage of nutrients based on your weather/nitrogen. The following tab is a work in progress and it has assumptions into it. Part of me is reluctant to share the soil part since it might create questions/confusion. The idea is to use soil test results to help develop a nutrient plan similar to the MLSN but with different values. Play around it with it and make it yours.

The main benefit to me is that I could map the file to my cell and plan PGR from a single chart. All of this fully automatic and visual.

PS I used a value of 200 in the PGR column to indicate when I applied PGR. Any value not null/0 will reset the GDD sum. 200 makes it easier to see the chart.

https://docs.google.com/spreadsheets/d/13qerLdtlO96lEdXpC6ixsmLu_EiK_jUaGqCQFX-yyuQ/edit?usp=sharing


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## Colonel K0rn

Nice work @g-man. Your spreadsheet is getting quite robust. Think you can get on the discord channel so I can work out the bugs for my setup?


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## drlushin

This video may have been linked previously in this thread, but I don;t think I saw it. It is from UNLTurf You Tube channel. You guys are so much smarter than me w/ all this stuff, but hopefully it might help someone else.

Also there are quick videos for setting up the greenskeeperapp for anyone that might be struggling w/ setup.

https://www.youtube.com/watch?v=XbNv5WKcMvM&index=11&list=PLwj31x_xFLeeWyG4XmpL2DUEkPM9CRm1E

Sounded like the synopsis of this video is

PGR Suppression Duration is affected by Air Temps & Mowing Frequency/Height
PGR Suppression Intensity is affected by Application Rate


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## drlushin

Enjoyed this as well

https://www.youtube.com/watch?v=hlEzwJZGs9o&index=5&list=PLwj31x_xFLeeWyG4XmpL2DUEkPM9CRm1E


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## drlushin

Found a User Guide for greenskeeperapp as well. Easily walks you through the setup and some of the functionality.

https://turf.unl.edu/greenkeeper/GreenKeeper-App-User-Guide.pdf


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## g-man

@GoPre I moved the conversation here so other could share their experiences.



GoPre said:


> Sweet. I am also going by GDD for primo. Do you guys plan on spraying 3 days out from target date since PGR takes a few to really kick in?





Pete1313 said:


> The way I interpret it is the target day is when you want to apply to avoid the rebound. So for a .3 oz/M rate I would reapply once the GDD counter reached 287 GDD base 0°C (516 GDD base 32°F). If I applied at a .4 oz/M rate I would reapply at 300 GDD base 0°C (540 GDD base 32°F). Those numbers are for KBG. g-man, do you agree?


I researched some time ago but did not post it. The short answer is that I think it should be applied *at * the GDD target, but rebound is still some GDD days out. The full cycle period for KBG is ~900 GDD. This means it goes into suppression, then into rebound up to no effect (a full cycle). The half way point (inflection point in the cycle) is the point when it transitions to rebound and it would be ~450 GDD. For sure we will need to apply the before this point. The peak suppression is around 225 GDD (0.25*900). So what the did is use the 30% (900*.3 =300). This places it in the upswing that I *think* allows for some time to absorb and start the cycle again. The rate affects the cycle period a little bit, that is why we have a slight different number for 0.3 rate vs 0.4 one.

Source of the 900GDD https://turf.unl.edu/PGR GDD Prov RI.pdf slide 9 bottom right chart. Source of the 0.3 * period, https://turf.unl.edu/PGR GDD Tracker v3.1.1.xlsm in the hidden sheets.

I'm approaching my reapplication date (15May) and of course the timing cannot be worst. My wife is out of town on a work trip, so I might need to apply it a day early or apply it after bedtime or get a babysitter so I could spray.


----------



## g-man

I ended up applying PGR the night of the 14 May at 0.5 rate. Looking at the app and my tracking, it is schedule to be applied 29May. That's just two weeks. It feels earlier but I'm going to stick to the schedule and see what happens.

I might up my rate to 0.6. I'm trying to figure out the rate at 1in for my NoMix. It is regulating, but not enough. Of course we have having great growing weather (Grow potential above 90% for the last weeks).

Who else is using the GDD model? What are your current observations? Impressions?


----------



## Pete1313

Im using it, but too early to tell. My first app was on 4/29 at .3 oz/M but it was with a 4 yr old bottle of podium I tried to finish off and didn't regulate at all. I reapplied on 5/14(alittle early by GDD time) with a fresh bottle of T-Nex at .4 oz/M and it's regulating like a champ right now. I'll report back in a few weeks. :thumbsup:


----------



## drlushin

I did my first app of T-Nex on 04/25/18. The greenskeeper app said I needed to reapply 05/15/18 which was 20 days. I reapplied 05/15/18 and the target date to reapply decreased to 05/30/18 so my duration of suppression shrunk by 5 days. It has been pretty warm during both of these time frames, but really really warm during this last cycle. This seems to be keeping in line w/ the fact that higher temps and mowing height effect the length of duration. I used 0.5oz/1K on my sodded Bermuda and 0.75oz/1K on my common bermuda. I can't speak to the intensity of Suppression due to quanity of PGR used. Even though I'm using different rates between sodded and common, the common grows almost 2-3 times as fast as the sodded.

I have been really impressed w/ the suppression especially on my Common Bermuda. That stuff grows up like wildfire compared to my sodded bermuda. The both seem to be growing up at a similar rate... which isn't very much. I went from 3 bags of clippings before PGR to 1/4 bag of clippings cutting at 1" once per week.

Just wanted to thank everyone for not only promoting the PGR, but all the wisdom shared. I've got a couple neighbors that keep asking how my grass is staying green yet growing so slowly.

Some days I feel like the TLF website pusherman in my neighborhood.


----------



## Thor865

I have Tifgrand. Using T-Nex. By reading label I should apply .2 oz/1k as I mow at about .5 hoc.

I'm using Greenkeeper app for tracking all apps of Fert, PGR, herbicides and such.

When inputting PGR it asks for GDD or to use default. I have a slight understanding of what GDD is and how it relates to reapplication rates based on weather data.

I am just looking for more of an explanation and how to properly input in GreenKeeper app.

Thanks!


----------



## Movingshrub

I would consider reaching out to the Syngenta rep and see if they have any remarks about Tifgrand and PGR dosage. I asked mine about recommended dosage for TifTuf and he laughed and told me TifTuf eats Primo-Maxx for lunch and to also take into consideration the HOC; higher HOC, less PGR, which was surprise to me. I know that doesn't address your GDD question but does impact the dosage.


----------



## J_nick

@Movingshrub per the label the higher the HOC the higher the recommended rate.

My lawn was 5/8" last year when I applied PGR at full rate for common Bermuda above 1/2" (.75oz/1000), it was not pretty. I basically didn't have to mow for a couple weeks and the lawn just looked sick. This year I'm at 3/8" and sprayed 8 days ago at .2oz/1000 and the grass is responding like it should.

To the OP. I'm also using the greenkeeperapp to track my PGR apps and the default was 225 GDDs, I know it changes with soil type and I assume it also changes with the selection of green, fairway, rough but not certain. I'm just going to roll with the 225 and see how it goes.


----------



## Movingshrub

J_nick said:


> @Movingshrub per the label the higher the HOC the higher the recommended rate.


I was surprised by the reps comment but just relaying the remark. His rational was that more leaf blade means more product absorbed.

I went with 0.38oz/1k as a starting amount on my backyard to see how the turf would handle it. I M also using the greenskeeper app. It's my first time using PGR so definitely a learning curve.


----------



## Ware

Movingshrub said:


> ...higher HOC, less PGR...


You must have been talking to the janitor - that is counter to every dosing trend across all turf types listed on their label...


----------



## Movingshrub

I did find a photo of the rep.


----------



## Colonel K0rn

I'd have to say that my experience so far using the blue pill method has been pretty spot on as far as gauging the regulation. I started seeing more clippings near the reapplication date of my PGR, and I was at 93% regulation, and only 10 GDD over 225. I was decided to do a slightly reduced application rate (first was 0.3 oz/M, second was 0.2 oz/M) this time, and the product was on the turf for just about 2 hours before rain came. I haven't had to mow yet, and that was 5 days ago, so it looks like the regulation percentage was a pretty accurate method for knowing when I'd need to reapply. Plus it's really really wet outside right now.


----------



## Tellycoleman

Ok I have 2 question about the green keeper app and GDD. I applied tnex and tide pacLo 2sl and entered them both into greenkeeper
Shouldn't the GDD be the same?
PacLo GDD since 19 of May is 143
Tnex GDD is 83 since May 19

What am I missing
Can someone explain

2) does anyone in the golf industry who uses primo and trimmit know the GDD for reapplication. Or do I apply each whenever the GDD is reached


----------



## g-man

Could you share a screenshot?


----------



## Turfguy93

Tellycoleman said:


> Ok I have 2 question about the green keeper app and GDD. I applied tnex and tide pacLo 2sl and entered them both into greenkeeper
> Shouldn't the GDD be the same?
> PacLo GDD since 19 of May is 143
> Tnex GDD is 83 since May 19
> 
> What am I missing
> Can someone explain
> 
> 2) does anyone in the golf industry who uses primo and trimmit know the GDD for reapplication. Or do I apply each whenever the GDD is reached


On bentgrass/poa putting greens primo is applied at 200 gdd and trimmit is applied at 300 gdd. If you are applying them together the rule of thumb is to use the the trimmit gdd. But the gdd are gonna be different(longer) on other taller mown species of grass


----------



## Tellycoleman




----------



## g-man

There is something wrong. The actual GDD should be the same since the product was applied the same day. The GDD threshold is different, but the actual should not be.

The actual GDD is just the sum of the temp above 32F (or 0C) for everyday since application. The greenskeeper app uses the data from a weather station close to your "course" location. If you only have one course, then you should only have one location and the GDD should be identical.

I've been tracking my own GDD in Google sheets reading the data from a station really close to me. The app is saying it also uses the same location, but we are off by 5-10 GDD. But, yours is way off.

Can you confirm you only have one course?


----------



## Tellycoleman

g-man said:


> There is something wrong. The actual GDD should be the same since the product was applied the same day. The GDD threshold is different, but the actual should not be.
> 
> The actual GDD is just the sum of the temp above 32F (or 0C) for everyday since application. The greenskeeper app uses the data from a weather station close to your "course" location. If you only have one course, then you should only have one location and the GDD should be identical.
> 
> I've been tracking my own GDD in Google sheets reading the data from a station really close to me. The app is saying it also uses the same location, but we are off by 5-10 GDD. But, yours is way off.
> 
> Can you confirm you only have one course?


I have done it 3 times when I get home I will screenshot and upload the video for evaluation. I believe the problem is with the greenkeeper app and the algorithm they use for Tide PacLo 2SC.
If you get a chance try to add that as a product and see if you don't get conflicting GDD.
When I use the name brand Trimmit 2SC then all GDD are the same. I added them all as an experiment into one application all in one tank into greenkeeper ( Primo Max- Trimmit - PacLo - and T-nex) All GDD we're identical except Tide PacLo 2SC. 
I think with the math there is an error in their source code. How do I contact Greenkeeper?



Can someone verify? I bet this is also why I was getting conflicting GDD when talking to @J_nick earlier this week
I have emailed greenkeeper with questions about this as well.


----------



## g-man

I have to do more research into some files excel files they published before the app. I'm on daddy duty and dont have the time.

I think the GDD in the Tide the app is using is GDD F instead of GDD C (83*9/5 = 149). The questions is why.


----------



## Green

Wow, not even sure where to begin. I don't even have a solid understanding of what GDD really is and how it works, let alone applying it to PGR intervals. @g-man, will probably PM you at some point...I need to figure out when my next app is due. I'm using 0.2oz/K on No-mix, TTTF/KBG, and PR/KBG, and I need to check to see when my first app was.


----------



## g-man

GDD = growing degree day

It is a tool used by gardening, farms and the msu prem model. You take the mean temp for that day and substract your base. For PGR the base is 0C/32F for cool season. The assumption is that as the mean is close to the base, the GDD is small and there is no much grow. When the mean goes to 86F (30C)then there is a lot of grow.

You sum the degree days (mean-base) for the days since your last application and reapply base of a value (~300). You then reset and start counting up again.

Ive made my tracking file available (post in this thread), but I do admit it is not simple. I'm doing other stuff with growth potential too. It is all based on the research from bill kreuser.

Create an account in the greenkeeper app and it tracks it for you. I think for a nomix you are too low at 0.2oz/K. I'm at 0.5oz and I'm at 1in hoc. If you are at 3in, I would go to 0.8 or even 1oz rate. The app will tell you how often to reapply based on the rate.


----------



## Green

Thanks. I started with a low level, because 2 years ago when I first started doing this, I over-regulated. And then last year, I got really bad rust partly because it was growing slowly, using 0.3oz on KBG/TTTF.

I've used GDD for help with scheduling pre-M apps, but I never really understood what it actually meant, and how it relates to soil and air temp.

If I can't figure out everything in time, I'll just reapply a bit before 3 weeks, since I'm using up old PGR right now. I'm hoping to get it figured out relatively easily, though.


----------



## Tellycoleman

I believe systemic fungicides have been known to increase PGR suppression when added to a plant controlled with Primmo Max.
Slowing down grows even more. Which is not what your really wanting when your trying to grow out a disease.


----------



## Turfguy93

Tellycoleman said:


> I believe systemic fungicides have been known to increase PGR suppression when added to a plant controlled with Primmo Max.
> Slowing down grows even more. Which is not what your really wanting when your trying to grow out a disease.


DMI fungicides such as propiconazole have growth regulating effects


----------



## viva_oldtrafford

Green said:


> Thanks. I started with a low level, because 2 years ago when I first started doing this, I over-regulated. And then last year, I got really bad rust partly because it was growing slowly, using 0.3oz on KBG/TTTF.
> 
> I've used GDD for help with scheduling pre-M apps, but I never really understood what it actually meant, and how it relates to soil and air temp.
> 
> If I can't figure out everything in time, I'll just reapply a bit before 3 weeks, since I'm using up old PGR right now. I'm hoping to get it figured out relatively easily, though.


IMO, measuring / monitoring yield is the easiest way of determining your re-apps. Whether it's on fairways (look at clippings left on the fairway post mow) or greens / tees (monitoring the amount of grass that my guys collect on their routes), motioning what you're left with after the mow gives you a good indicator of where you stand. Of course, the method means that you need to mow multiple times a week, but it is a very accurate alternative to GDD if you can recognize increases in clip yield.


----------



## Green

Well, I can tell the grass is coming out of regulation right now, just by looking at it. Having 90 degrees today didn't help. And I looked back on the calendar. Sure enough, it's a couple days past 3 weeks. Can't believe how that snuck up on me. Unfortunately, I can't spray until Monday. I'm hoping I don't get a full-fledged rebound effect...doesn't that stress the grass?

Wish I'd found this thread beforehand.


----------



## g-man

If you enter the info in greenskeeper app for the last app you did (3 weeks ago), it should tell you if you are in rebound (negative suppression).


----------



## dtillman5

So this may be a dumb question but if you are combining PGR with FAS, could you still follow GDD for PGR and keep FAS in the mix? Also in one of John Ware's recent YouTube videos he mentioned possibly no ill effects from PGR on wet/dew grass, could this hold true for FAS too?


----------



## g-man

Great question. Since gdd is variable, you will need to adjust your rate of FAS to match or do it separately.


----------



## dtillman5

g-man said:


> Great question. Since gdd is variable, you will need to adjust your rate of FAS to match or do it separately.


 well at least I can tank mix the first app but once GDD kicks in may have to space it out


----------



## GoPre

g-man said:


> @GoPre I moved the conversation here so other could share their experiences.
> 
> 
> 
> GoPre said:
> 
> 
> 
> Sweet. I am also going by GDD for primo. Do you guys plan on spraying 3 days out from target date since PGR takes a few to really kick in?
> 
> 
> 
> 
> 
> 
> Pete1313 said:
> 
> 
> 
> The way I interpret it is the target day is when you want to apply to avoid the rebound. So for a .3 oz/M rate I would reapply once the GDD counter reached 287 GDD base 0°C (516 GDD base 32°F). If I applied at a .4 oz/M rate I would reapply at 300 GDD base 0°C (540 GDD base 32°F). Those numbers are for KBG. g-man, do you agree?
> 
> Click to expand...
> 
> I researched some time ago but did not post it. The short answer is that I think it should be applied *at * the GDD target, but rebound is still some GDD days out. The full cycle period for KBG is ~900 GDD. This means it goes into suppression, then into rebound up to no effect (a full cycle). The half way point (inflection point in the cycle) is the point when it transitions to rebound and it would be ~450 GDD. For sure we will need to apply the before this point. The peak suppression is around 225 GDD (0.25*900). So what the did is use the 30% (900*.3 =300). This places it in the upswing that I *think* allows for some time to absorb and start the cycle again. The rate affects the cycle period a little bit, that is why we have a slight different number for 0.3 rate vs 0.4 one.
> 
> Source of the 900GDD https://turf.unl.edu/PGR GDD Prov RI.pdf slide 9 bottom right chart. Source of the 0.3 * period, https://turf.unl.edu/PGR GDD Tracker v3.1.1.xlsm in the hidden sheets.
> 
> I'm approaching my reapplication date (15May) and of course the timing cannot be worst. My wife is out of town on a work trip, so I might need to apply it a day early or apply it after bedtime or get a babysitter so I could spray.
Click to expand...

@g-man I just saw this post, I am so sorry for ignoring you. That is very interesting information, and I just learned something. Thanks so much.


----------



## g-man

@Tellycoleman I checked the files. For paclobutrazol 25C, they used a GDD threashold of 260 GDD 0C Therefore I think this a bug in their system.


----------



## Tellycoleman

g-man said:


> @Tellycoleman I checked the files. For paclobutrazol 25C, they used a GDD threashold of 260 GDD 0C Therefore I think this a bug in their system.


Yes I just got a reply last night from greenkeeper. 
I will copy and paste. Hopefully they will fix it quickly

Telly,

You're right, it is using base 0C (cool-season) instead of base 10C for your bermudagrass greens. I'll get that changed. Are you using paclo on your greens? How does it work?

Bill

They responded very quickly on Memorial Day.
Nice!!!!


----------



## g-man

That's likely Bill Kreuser himself. I would tell him that it is just your house "greens" and invite him to TLF.


----------



## Green

g-man said:


> If you enter the info in greenskeeper app for the last app you did (3 weeks ago), it should tell you if you are in rebound (negative suppression).


I looked at the app online, and the website wasn't secure. How far back does it allow you to go? It does not appear I entered into too bad of a rebound yet, thankfully. The 2nd app went down the other day. I upped the rate to half rate.


----------



## g-man

PSA, check your data.

I dont understand why they only sent a twitter announcement instead of an email for something this important (bad data). They had an issue with getting the data from weather underground (no surprise there). You need to tweak/edit the data in the greenkeeperapp manually to fix it.

https://twitter.com/GreenKeeperApp/status/1013615777512083456


----------



## Ware

That is odd that they would only post that on Twitter - also that they stated the wrong month: _The issue started on July 29th._

Looks like mine is definitely missing June 29 data:

















One day of missing data only changed my application schedule by one day, but it's definitely a good reminder to double check the weather data coming in.

















And it looks like they are working on some solutions:

https://twitter.com/GreenKeeperApp/status/1013750882478026757​


----------



## Redtwin

I applied T-Nex to my Bermuda today. The label says to use .38 oz/K for Tifway 419. Since I have been mowing around 1/2", and the fact that this is my first time using a PGR, I decided to go with the lower rate of .25oz/K. I'm using Greenskeeper app to track my application. Shouldn't there be a difference in total GDD for the lower app rate. It's showing 225 GDD. I thought that was the same as when I did a test run at .38 with Greenskeeper. Does it automatically adjust the GDDs based on rate or will I have to keep an eye out for a rebound? Thanks for any help from all you experienced PGR guys. I want to join the club.


----------



## Durso81

So I don't know how greenskeeper calculates everything, but I used it last year and did the same started off low. And followed greenskeeper when it said to apply and never had a rebound. Also from my experience there is wiggle room. There was a time last year where I couldn't apply when I needed to and I was a week late applying and had no rebound.


----------



## J_nick

I believe no mattter the rate the AI stays in the plant the same amount of time. Varying the amount will vary the amount of suppression you get not the time.


----------



## smurg

J_nick said:


> I believe no mattter the rate the AI stays in the plant the same amount of time. Varying the amount will vary the amount of suppression you get not the time.


The Quali-pro label for T-nex states the opposite; more product increases the length of suppression, not the level of suppression:



Without knowing much about plant biology and just thinking out loud about it, I would agree with you since half-lives and such would remain the same. I should download a copy of the Primo Maxx label to see if they have any tidbits on this topic.


----------



## Redtwin

Thanks for the feedback everyone. I'm still really nervous about messing up the rate. I calibrated my sprayer 3 times worrying about whether or not I would overdo it. It came out perfect though. I had about a half cup left over and just sprayed that around some of the edging.


----------



## Ware

Redtwin said:


> I applied T-Nex to my Bermuda today...


Merging this thread.


----------



## g-man

We had a similar conversation in the cool season side. I'm cross posting here:

I used Bill Kreuser data to develop this chart. I checked it the greenkeeperapp last year. I need to check if they changed the values.

For greens hoc, the gdd threshold is constant, for others it all follows this chart. It might be from the lack of research (higher hoc).



In tabular format:
From the GreenKeeper Website 
T-Nex rate	GDD 0C Threshold	
0.125	261	
0.25	280	
0.3	287	
0.35	294	
0.4	300	
0.5	317	
0.55	323	
0.6	330	
0.75	353	
0.8	360	
1	389


----------



## gm560

g-man said:


> @GoPre I moved the conversation here so other could share their experiences.
> 
> 
> 
> GoPre said:
> 
> 
> 
> Sweet. I am also going by GDD for primo. Do you guys plan on spraying 3 days out from target date since PGR takes a few to really kick in?
> 
> 
> 
> 
> 
> 
> Pete1313 said:
> 
> 
> 
> The way I interpret it is the target day is when you want to apply to avoid the rebound. So for a .3 oz/M rate I would reapply once the GDD counter reached 287 GDD base 0°C (516 GDD base 32°F). If I applied at a .4 oz/M rate I would reapply at 300 GDD base 0°C (540 GDD base 32°F). Those numbers are for KBG. g-man, do you agree?
> 
> Click to expand...
> 
> I researched some time ago but did not post it. The short answer is that I think it should be applied *at * the GDD target, but rebound is still some GDD days out. The full cycle period for KBG is ~900 GDD. This means it goes into suppression, then into rebound up to no effect (a full cycle). The half way point (inflection point in the cycle) is the point when it transitions to rebound and it would be ~450 GDD. For sure we will need to apply the before this point. The peak suppression is around 225 GDD (0.25*900). So what the did is use the 30% (900*.3 =300). This places it in the upswing that I *think* allows for some time to absorb and start the cycle again. The rate affects the cycle period a little bit, that is why we have a slight different number for 0.3 rate vs 0.4 one.
> 
> Source of the 900GDD https://turf.unl.edu/PGR GDD Prov RI.pdf slide 9 bottom right chart. Source of the 0.3 * period, https://turf.unl.edu/PGR GDD Tracker v3.1.1.xlsm in the hidden sheets.
> 
> I'm approaching my reapplication date (15May) and of course the timing cannot be worst. My wife is out of town on a work trip, so I might need to apply it a day early or apply it after bedtime or get a babysitter so I could spray.
Click to expand...

Sorry for reviving an old thread here. Does anyone have a copy of the excel workbook reference above? The link no longer works. I know its available through the app, but was hoping to get more detail about the underlying calculations


----------



## Ware

Here is a recent article about GDD from Bill Kreuser, PhD.

The Nuance of Growing Degree Day Calculations - February 18, 2020 by GreenKeeperApp


----------



## Coach8

I'm about to make my first foray into spraying T-Nex. I am using the greenkeeper app. It only has Bermuda as an option, no qualifiers as to hybrid or common. With my common bermuda rate being 2-3x what many hybrid types require, is that going to throw off my GDD?


----------



## HoosierLawnGnome

My experience on KBG is to hit it right at greenup and keep on it before it needs it.

I'm not a huge fan of busting out the calculator and calendar to figure out when it needs reapplication. I look at the grass and track how much its growing based on how frequently I mow. Too many immediate environmental changes affect it, and HOC makes a big difference too.

I dont have enough control to make it that predictable, particularly if my schedule may not allow me to put it down at the ideal time anyways. So i always opt for going early and being careful to watch how much I apply.

This year I'm not using it at all. Better for me not to use it given all my factors right now.


----------



## Ware

Coach8 said:


> I'm about to make my first foray into spraying T-Nex. I am using the greenkeeper app. It only has Bermuda as an option, no qualifiers as to hybrid or common. With my common bermuda rate being 2-3x what many hybrid types require, is that going to throw off my GDD?


It shouldn't matter. The User Guide says:



> GreenKeeper will automatically calculate the ideal PGR GDD re-application interval based on the PGR selected, application rate, grass species, and management type (i.e. greens vs tees vs roughs). All of these factors influence the longevity of a PGR application. Leave the 'Custom GDD' box blank to use the default interval calculated by GreenKeeper.


But from what I have seen it defaults to 225 GDD for bermuda, regardless of application rate. So you should be good to go with however much T-Nex you apply to achieve the suppression you desire. If you find the default 225 GDD needs to be adjusted, you can enter a custom GDD value when you add T-Nex to your application in the app.


----------



## JRS 9572

@Ware any rule of thumb on WHEN you should start applying during the growing season? I'm just at an average of 65F for soil temp. here in South Carolina.


----------



## Ware

JRS 9572 said:


> @Ware any rule of thumb on WHEN you should start applying during the growing season? I'm just at an average of 65F for soil temp. here in South Carolina.


I usually don't start applying PGR until I am needing to mow more than once a week.


----------



## Mightyquinn

Ware said:


> JRS 9572 said:
> 
> 
> 
> @Ware any rule of thumb on WHEN you should start applying during the growing season? I'm just at an average of 65F for soil temp. here in South Carolina.
> 
> 
> 
> I usually don't start applying PGR until I am needing to mow more than once a week.
Click to expand...

+1 :thumbup:


----------



## Alex_18

@Ware @Mightyquinn

So just to be clear, when do i re apply according to the greenkeeper app? According to the lifespan? And how soon before, 1 day, a few days, a week, etc? Thanks in advance. I just did my first app of t nex on the 10th so im still trying to figure it all out

I can tell its working already because i cut yesterday which was 6 days after my last cut. Used to cut every 3 days. I was taking off about the same, maybe even less yesterday with twice the time in between cuts


----------



## Mightyquinn

I usually try to apply it within a 2-3 day window on either side of the "expiration" date that the Greenskeeper app says.


----------



## Colonel K0rn

Coach8 said:


> I'm about to make my first foray into spraying T-Nex. I am using the greenkeeper app. It only has Bermuda as an option, no qualifiers as to hybrid or common. With my common bermuda rate being 2-3x what many hybrid types require, is that going to throw off my GDD?


One of the things I found my first year that I sprayed PGR, is that I went a little light on my rate, and when I saw that I was physically collecting more clippings, I calculated the number of GDD's that had passed, along with the rate that Greenskeeper was showing. I was coming out of suppression faster than I "should" have been, so I needed to up my rate some more. I've got it dialed in now, and am having great luck with it. Just remember, it's like salt in a recipe... you can always add more, just can't remove it.


----------



## Coach8

Colonel K0rn said:


> Coach8 said:
> 
> 
> 
> I'm about to make my first foray into spraying T-Nex. I am using the greenkeeper app. It only has Bermuda as an option, no qualifiers as to hybrid or common. With my common bermuda rate being 2-3x what many hybrid types require, is that going to throw off my GDD?
> 
> 
> 
> One of the things I found my first year that I sprayed PGR, is that I went a little light on my rate, and when I saw that I was physically collecting more clippings, I calculated the number of GDD's that had passed, along with the rate that Greenskeeper was showing. I was coming out of suppression faster than I "should" have been, so I needed to up my rate some more. I've got it dialed in now, and am having great luck with it. Just remember, it's like salt in a recipe... you can always add more, just can't remove it.
Click to expand...

Great point.


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## Jairow

Just started using the Greenkeeper app after my first T Nex application. Are you all manually entering weather data? The weather in my area was defaulted to 32F and I was showing suppression forever. Once I manually edited the weather data with today's temperature, I got a lifespan of 14 days with my rate of 0.20 oz/1k, which seemed reasonable.

I thought maybe the lack of weather info was due to my small town. I changed the Zip Code to larger cities, San Antonio, Dallas, but still weather data was defaulted to 32F.


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## desirous

Jairow said:


> Are you all manually entering weather data? The weather in my area was defaulted to 32F and I was showing suppression forever.


No, it works as expected for me, pulls the weather data.


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## ScottW

My recollection from when I started using greenkeeper last year is that it starts tracking weather data from the date you sign up, but doesn't retrieve data prior to that. You can add that manually, but you shouldn't have to for PGR since you start at GDD of 0 anyway when you spray an app. As more days go by, it will collect more real data, and should develop an accurate estimate of application lifespan before you have to spray again.


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## Jairow

Thanks for the replies. I've been using it over a week now and it's hit or miss with automatically updating the weather. I can readily tell when the weather doesn't automatically update as it adds one or two days to my original GDD after application. With no drastic change in weather, I pretty much know that I have about 14 days of suppression with temperature averages in the low 80s.


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## Meatpopsickle

Recently purchased tnex and applied half rate (.125oz/1000) after reading quite a bit on those who have applied their first application with some yellowing etc. using the UNL GDD tracker. First application was 6/22. Based on weather forecast I would be applying Tnex again on 6/30.

Could this be right?

Daytime temperatures are hovering around 110 currently with night time Lows in 80s.

Tracker doesn't allow me to adjust application rate. Should I assume that my half rate application would really mean I'm reapplying in 4 days rather than 8?


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## g-man

Rate of product barely affects reapplication time. Temperatures is the biggest factor. With a 110F temps you will be applying more often.


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## Meatpopsickle

g-man said:


> Rate of product barely affects reapplication time. Temperatures is the biggest factor. With a 110F temps you will be applying more often.


Guess it's a good thing I have a gallon of this stuff. Just seemed crazy that tangos would be in 8 day intervals. Then again it is hot as hell here...


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## g-man

You can add another pgr to get you more suppression. I think palco. Ask in the warm season folder. I don't know much about warm season stuff.


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## wiseowl

So I finally got my first app of PGR down two days ago and I'm already impressed with the outcome, wish I had done it earlier in the season but with freshly laid sod wasn't sure it was a good idea.

Question, I've got warm season Tif419, Southern California, when should my last app be and how do I deal with the rebound before it goes dormant for winter ?

I was thinking 1 more application when the GDD finishes off in probably mid September and then deal with the rebound effect into October and then let it hang out, maybe one more fert before "winter" depending on how it's looking.

To add more complexity, I know I'm thinking ahead, I also am starting to research an overseed with perrenial rye and when/how to do that to try and keep the lawn green through the cool rainy season. I would assume still no pgr and no fert for cool season over Bermuda. It I'm still researching.


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## marcjw

Just curious what the recommended GDD would be for T-nex applied to zeon zoysia warm season climate? I'd be applying the low rate.


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## marcjw

To get Greenkeeper app to track GDDs do you have to upgrade to premium?


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## g-man

No you don't. I tagged you in a thread on how to setup the greenkeeperapp.


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## steffen707

I read how to calculate GDD here https://extension.psu.edu/understanding-growing-degree-days
and also how you can get GDD spit out for you here, https://www.greencastonline.com/growing-degree-days/home
But what I haven't read with people Quoting GDD of 2XX for this grass and 3XX for that grass. Does this mean you calculate your daily GDD number, and cumulative GDD number since last application of a PGR, and when your cumulative number is about to exceed the GDD for your given turf type, you would want to reapply the PGR?

Essentially forecasting the amount of supression ability/power that is left from the PGR application, based on temps and your type of grass? Then based on the research of GDD you can forecast when to reapply the PGR so that you're actually a few days ahead of its rebound so you're consistently supressing the grass growth without over applying, or letting it start growing again?

Oh and I looked into Greenkeeper, I don't think they have a free version anymore.


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## Lawn Burgundy

g-man said:


> In tabular format:
> From the GreenKeeper Website
> 
> T-Nex rate	GDD 0C Threshold
> 0.125 261
> 0.25 280
> 0.3 287
> 0.35 294
> 0.4 300
> 0.5 317
> 0.55 323
> 0.6 330
> 0.75 353
> 0.8 360
> 1 389


@g-man does this translate directly (1 to 1) to the 10c with warm season? as far as GDD's are concerned?


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## g-man

I dont know. I think bermuda is a fixed GDD of 200.


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