# PGR AND GROWING DEGREE DAYS



## JRS 9572 (May 28, 2018)

Is there anywhere that gives a simplistic "cliff notes" version of how to look at growing degree days and figure when you put down your 1st application, and subsequent applications?

Tried the search section and came up empty handed. I know there has to be a huge thread on this.


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## tommyboy (Aug 20, 2019)

Try this. You'll have to put your zip code in.
http://www.greencastonline.com/tools/soil-temperature


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## Ware (Jan 28, 2017)

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


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## Redtwin (Feb 9, 2019)

I use greenkeeperapp.com . Despite the name, it's not an app but a website. It'll track GDD for you and let you know when to reapply.


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## 1FASTSS (Jul 11, 2018)

Redtwin said:


> I use greenkeeperapp.com . Despite the name, it's not an app but a website. It'll track GDD for you and let you know when to reapply.


This is what I will use too...but I most likely wont start until later this summer. I'm tracking my shaded areas this year and want to see where my final landscape bed edges will be :lol:


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## JRS 9572 (May 28, 2018)

Thanks folks. I'll research better. I am going on the app. I think @Ware link will help me understand what the growing degree days mean, and when it signals it's time. I'm slow on the uptake on how it's figured, and what it means.

Thanks again for the help.


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## Ware (Jan 28, 2017)

JRS 9572 said:


> Thanks folks. I'll research better. I am going on the app. I think @Ware link will help me understand what the growing degree days mean, and when it signals it's time. I'm slow on the uptake on how it's figured, and what it means.
> 
> Thanks again for the help.


It's a simple calculation, but gets confusing because there are different base temps used for calculating GDD's. I think the GreenKeeper app uses a base of 0°C for cool season turf and a base of 10°C for warm season turf. The app basically just uses your local weather to add up GDD's until you get to your designated PGR reapplication interval (e.g. 225 GDD).


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## cglarsen (Dec 28, 2018)

I think in the Carolinas by the time you need PGR you could get by with applying every 20 days if you wanted to keep it stupid simple. I saw the rebound begin right around 3 weeks last July/Aug.


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## Ware (Jan 28, 2017)

This is what the suppression curve looks like:










Note it takes a few days after application to reach peak suppression (the lowest point on the relative clipping yield curve). By hedging your apps (applying several days ahead of the rebound phase), your previous app is wearing off as your next app is ramping up - keeping the relative clipping yield below 100%. Probably around day 12 in the scenario above.

Counting GDD's is just a tool to help you estimate where you are in the suppression curve/phase, recognizing that the "Days After Application" axis is really variable based on weather conditions.


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## ShaneQi (Oct 9, 2019)

Hello guys, started using Greenkeeper App and it's amazing!

Quick question:
I added an application of T-nex at the rate of 0.75 oz/ksqft, I was expecting the GDD be automatically changed to 1200 because the default is: rate 0.125 oz/ksqft GDD 200, but the GDD is still at 200.
So I assume rate has nothing to do with GDD, is that correct? Or it does and I'm supposed to change GDD manually?

I also noticed that when I add an application with other products (e.g. dimension), reapplication interval doesn't change as I change rate, either. I'm pretty sure dimension's rate has something to do with reapplication interval. Does that mean that the default reapplication interval is supposed to be changed manually as I change rate?


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## Redtwin (Feb 9, 2019)

.75 sounds SUPER heavy for Bermuda. I'm not looking at the T-Nex label but I think the default is .38oz/1000sf; I mow low (.3" HOC) so I apply .25oz/1000sf. I also manually change the GDD to 250. I let it fully run out and then apply the next free day I have. You usually have a little wiggle room before it starts to rebound.

When you mix in a product, you will get the screen that allows you to adjust the rate of application and the reapplication interval for each product you mix in.


Edit: I obviously didn't change the GDD default to 250 on this one but I still let it run out all the way.


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## ShaneQi (Oct 9, 2019)

@Redtwin

Thanks for sharing. T-next label says 0.75oz/ksqft, but I'm also doubtful about it because other grass doesn't need even as close to that rate.

This is gonna be my first PGR application ever, I'll probably use say 0.5 and observe.


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## cutigers08 (Aug 16, 2019)

Great call on greenkeeperap.com. Set up a profile today!


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## Redtwin (Feb 9, 2019)

ShaneQi said:


> @Redtwin
> 
> Thanks for sharing. T-next label says 0.75oz/ksqft, but I'm also doubtful about it because other grass doesn't need even as close to that rate.
> 
> This is gonna be my first PGR application ever, I'll probably use say 0.5 and observe.


Good call on the .5oz/1000sf, especially on the first app. I actually checked the label after seeing another member post about using .75. The label shows .75oz for common bermuda. I have Tifway 419 so that is why my rate is lower. I still get way better response than expected so that is why I let it run all the way out. I actually went out to 300 GDD last year and still didn't have much of a rebound.


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