# GDD and this HEAT



## Tellycoleman (May 10, 2017)

So im just wondering what you guys are doing as far as the short window that GDD gives you for reapplication because of this heat!!!!
Those guys with 100 degree plus days are suggested to reapply every 7-9 days according to GDD calculations?
DO you still try to stay on a ruffly 14 day schedule? Or do you strictly follow reapplication at 200 GDD of T-nex.


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## Ware (Jan 28, 2017)

Timely discussion. I just reapplied this morning...

​
I think I exceeded my 1 gallon/thousand carrier rate - I didn't account for sweat...

​


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## TN Hawkeye (May 7, 2018)

Sorry for being ingnorant, but what is GDD?


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## Tellycoleman (May 10, 2017)

Yeah my Daily GDD yesterday was 29.9 F
High Yesteday was 101
Hey its a good weight loss program. Forget Hot Yoga!


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## Tellycoleman (May 10, 2017)

TN Hawkeye said:


> Sorry for being ingnorant, but what is GDD?


Growing degree days
Basicaly its a calculation based on the weather on how long your PGR will last. The science behind it states that the hotter it is the shorter your PGR will last.


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## Spammage (Apr 30, 2017)

Tellycoleman said:


> Yeah my Daily GDD yesterday was 29.9 F


Only 30?? DFW was 34 yesterday and 40 on Tuesday. I don't use GDD for this reason. Suppression lasts longer than the GDD data would indicate in my experience, so I still plan on 21 day intervals. If a rebound starts ahead of that time frame, then I will adjust accordingly.


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## Tellycoleman (May 10, 2017)

You might be comparing Celsius GDD with ferinheight. Also GDD is based on daily average. We started yesterday in the 70's. 
Then again I don't claim to be an expert. Every time I post something about my GDD I get someone telling me WTF. Lollol so I just try to use the green keeper app and stick with it.


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## Ware (Jan 28, 2017)

Suppression definitely extends beyond the ~225 GDD threshold, but data suggests that's the point where clipping yield begins to increase, so the theory is that maximum suppression can be achieved by hedging with another application at the point where the clipping yield curve begins to inflect upward. trc illustrated it well with his mspaint skillz in this post:



trc said:


> My $0.02 as a new pgr applicator and greenkeeperapp user but have read a UNL research paper or two...
> 
> Suppression percentage begins to decrease at the conclusion of the gdd calculated lifespan and is the recommended reapplication point. However, "full rebound" where clipping yield is greater than without PGR may not occur in the model for up to several hundred additional gdd.
> 
> I conclude there is a buffer to apply beyond 100% lifespan and avoid "full rebound". However, hitting the target date optimizes full suppression between apps by smoothing out the decrease in suppression from the old app with the incremental increase in suppression on the new app - full suppression on the new app is available approximately when the old app has reached "full rebound". See mspaint skills below:


I was skeptical at first, but it is working well for me - so I plan to continue using the GDD model for my PGR apps. :thumbsup:


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## Spammage (Apr 30, 2017)

Tellycoleman said:


> You might be comparing Celsius GDD with ferinheight. Also GDD is based on daily average. We started yesterday in the 70's.
> Then again I don't claim to be an expert. Every time I post something about my GDD I get someone telling me WTF. Lollol so I just try to use the green keeper app and stick with it.


No, those are GDD for DFW. Dallas Love Field shows Tues was 104° high, 82° low, and 42 GDD. I dabbled with the greenkeeper app, but unless it is reporting GDD in a different way, it would have me reapplying every 6-7 days.


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## Spammage (Apr 30, 2017)

Ware said:


> Suppression definitely extends beyond the ~225 GDD threshold, but data suggests that's the point where clipping yield begins to increase, so the theory is that maximum suppression can be achieved by hedging with another application at the point where the clipping yield curve begins to inflect upward. trc illustrated it well with his mspaint skillz in this post:
> 
> 
> 
> ...


Ok, so roughly 450-500 reapplication based on trc's supplied table. At least that would make my apps 12-15 days apart. That at least gets a little more palatable, but I still believe the eye test is the best method. My Palisades always tells me when reapplication is needed, so my El Toro and little bit of bermuda stay in full regulation.


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## J_nick (Jan 28, 2017)

Spammage said:


> Tellycoleman said:
> 
> 
> > You might be comparing Celsius GDD with ferinheight. Also GDD is based on daily average. We started yesterday in the 70's.
> ...


Greenkeeperapp uses GDD's in Celsius normally around 225-250 for reapplication intervals.

The numbers you posted are for GDD's in Fahrenheit. So your reapplication interval would be 405-450 GGD's for °F


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## g-man (Jun 15, 2017)

@Spammage It will be interesting to collect clipping yield data for your weather. I'm not sure how far south the model was used, but I think it should still work.


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## Ware (Jan 28, 2017)

Spammage said:


> Ok, so roughly 450-500 reapplication based on trc's supplied table...


No, my interpretation of trc's table is that 450 GDD would be the point where relative clipping yield returns to 1.0 (the horizontal dotted line) and the turf is transitioning into rebound - where clipping yield is actually greater than when not using PGR. His table illustrates why 225-250 GDD (Greenskeeper uses base 10°C for warm season turf) might be the ideal time to reapply.


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## Spammage (Apr 30, 2017)

Ok. I may pull it back up and run it to see how it compares to my observations. As I'm seeing the conversion, 40°f roughly equates to 22°C. @Ware are you applying every two weeks, or have the numbers been closer to three weeks?


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## Tellycoleman (May 10, 2017)

Spammage said:


> Tellycoleman said:
> 
> 
> > Yeah my Daily GDD yesterday was 29.9 F
> ...


I dont understand? WHat is the reason you dont use GDD. I dont think there is any discrepancy. Doing calculations My high 100 low 71.6 so my average temp (which is what GDD is based on) was 85.8F which equals and increase of 29.9 GDD
Your daily average was alot higher than mine you started your day 10 degrees hotter than me. So your average is at 93F (High of 104 low of 82) So your GDD on feringeight scale is 33.9.
But to each his own. I am not gonna say your system which has been working for you is wrong.

To add another monkey in the wrench I use 2 types of PGR which comes to 40cc T-Nex and 40cc Paclo (0.22 floz per 1000) per spreader mate fill up(6,000ft).. I know i supposed to use a higher rate of paclo but im playing it safe since @Greendoc told me paclo can lead to over suppression . From what i read golf courses way down south mix Paclo in with Tnex when it gets so hot that GDD suggest reapplication every 7 days.


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## Ware (Jan 28, 2017)

Spammage said:


> ...Ware are you applying every two weeks, or have the numbers been closer to three weeks?


Using Greenskeeper, my last 2 apps (before today's app) were at 12-13 day intervals at a rate of 0.25 oz/M. This is what my daily GDD's (10°C base) looked like during that period:








Here is a link to that calculator.

Here is another article/chart on the Australian Syngenta site that discusses using GDD's to choose the optimal time for re-application. I think there must be something to it if Syngenta is talking about it - or maybe they just want us to buy more Primo :lol: .








The actual location of the inflection point of the Relative Clipping Yield curve would be difficult to determine without weighing clippings, but I think there is some merit to the shape of that curve. For example, the Primo label states that full growth regulation begins at about 3-5 days after application, so to me it makes sense to reapply 3-5 days before relative clipping yield returns to normal. Doing so essentially levels the suppression rate. This is what the chart above would look like with subsequent applications (red) at 10, 20 and 30 days:


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## Spammage (Apr 30, 2017)

Tellycoleman said:


> WHat is the reason you dont use GDD. I dont think there is any discrepancy. Doing calculations My high 100 low 71.6 so my average temp (which is what GDD is based on) was 85.8F which equals and increase of 29.9 GDD
> Your daily average was alot higher than mine you started your day 10 degrees hotter than me. So your average is at 93F (High of 104 low of 82) So your GDD on feringeight scale is 33.9.
> But to each his own. I am not gonna say your system which has been working for you is wrong.


I'm certainly not saying they are wrong about the GDD model or even the reapplication timing, and I'm not saying I'm right. My system and dosing works for me for 3 week reapplication instead of two. My Palisades zoysia does come out of regulation, but my other grasses don't, including El Toro zoysia, so I assume that different bermuda cultivars would also behave similarly in that they would respond differently to rates and timing.

I know that Irias noted that Celebration doesn't like Primo apps over .25oz/K, where I'm using .4oz/K on even my zoysia. I also think @viva_oldtrafford even mentioned the eye test as being the most sound way to know when to reapply.

I would like to see this work and may give it another shot. I do wish that this was an app I could use on my phone. If that is possible, then it may win me over.


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## g-man (Jun 15, 2017)

@Spammage The greenkeeperapp is used on any web browser including phones.

This ppt slide explains the model in a lot of detail. https://turf.unl.edu/PGR%20GDD%20Prov%20RI.pdf Page 4 and 5 have how the clipping yields looks if applied every 4 weeks, 800 GDD, 400 GDD and 200 GDD. Look how it stays in suppression at 200GDD (top left page 6).

The best way to do this is to collect clipping data, but none of us want to do that too.


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## viva_oldtrafford (Apr 4, 2018)

Spammage said:


> Tellycoleman said:
> 
> 
> > WHat is the reason you dont use GDD. I dont think there is any discrepancy. Doing calculations My high 100 low 71.6 so my average temp (which is what GDD is based on) was 85.8F which equals and increase of 29.9 GDD
> ...


Nothing beats daily monitoring and clip yield monitoring.


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## Spammage (Apr 30, 2017)

g-man said:


> @Spammage The greenkeeperapp is used on any web browser including phones.
> 
> This ppt slide explains the model in a lot of detail. https://turf.unl.edu/PGR%20GDD%20Prov%20RI.pdf Page 4 and 5 have how the clipping yields looks if applied every 4 weeks, 800 GDD, 400 GDD and 200 GDD. Look how it stays in suppression at 200GDD (top left page 6).
> 
> The best way to do this is to collect clipping data, but none of us want to do that too.


 :thumbup: I initially looked in the app store for a mobile app and came up empty. I ended up setting up an account on my PC (which gets used about once a month anymore), but never checked again with my phone. I've only recorded fertilizer apps to this point, but will record my next primo app and see how it goes. Has anyone paid for the premium app?


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## randy (Jun 29, 2018)

This was my first PGR application and I hit my lawn with a lower rate just to ease into it. It's funny, because it already seems to be wearing off.

I can't win.


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## randy (Jun 29, 2018)

@Ware is there an app you use to keep track of your lawn applications and all the variables surrounding it? Based on your screenshot, I figured maybe you did. If not, would be cool for some of us to develop an affordable one that home owners and professional turf managers could use.



Ware said:


> Timely discussion. I just reapplied this morning...
> 
> ​
> I think I exceeded my 1 gallon/thousand carrier rate - I didn't account for sweat...
> ...


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## Ware (Jan 28, 2017)

randy said:


> Ware is there an app you use to keep track of your lawn applications and all the variables surrounding it? Based on your screenshot, I figured maybe you did. If not, would be cool for some of us to develop an affordable one that home owners and professional turf managers could use.


That is from the Greenskeeper app. I track all my apps in a spreadsheet though. It's not pretty, but logs the info I want to track (date, product, rate, and cumulative totals of macro/micronutrients, etc).


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## Spammage (Apr 30, 2017)

Okay, I applied at dusk on Friday evening, and so as to avoid counting Friday's GDD #s, I input the app as a Saturday app 7/14. The app is showing the lifespan to 7/27. Have most of you been applying early to account for the 3-5 day full suppression, or applying on the date of the lifespan end?


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## gatormac2112 (Sep 14, 2017)

My lifespan is showing 7/14-7/29.

GDD calculation brought to you by the makers of T-Nex and Primo :lol:


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## g-man (Jun 15, 2017)

@Spammage Apply at the date. They already accounted for the 3-5 days for suppression.


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## Spammage (Apr 30, 2017)

g-man said:


> @Spammage Apply at the date. They already accounted for the 3-5 days for suppression.


Thank you sir!


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