# PGR newbie - re-application time?



## davegravy (Jul 25, 2019)

...if I understand correctly I should look at re-applying in the next few days else I'll start to get a rebound effect (grass that grows like mad)?


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## Harts (May 14, 2018)

@davegravy use the GDD tracker as a guideline. I have pushed my timing before and didn't experience excessive growth. Let it get to 100% and check your grass. Depending on your rates, your suppression might last longer than the tracker suggests.


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## g-man (Jun 15, 2017)

Apply when the GDD reaches 279. They are predicting that's going to be 30May. +/- 2 days is fine.


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## Babameca (Jul 29, 2019)

g-man said:


> Apply when the GDD reaches 279. They are predicting that's going to be 30May. +/- 2 days is fine.


A bit off topic, but I am sand dressing and mine is also wearing out. Do I skip in order to use the rebound, or it will make my continuous 'brushing in' job (which I plan to carry on for a few days) more difficult?


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## g-man (Jun 15, 2017)

Or do more nitrogen. Too many options. It is hard to pick.


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## bhutchinson87 (Jun 25, 2018)

Harts said:


> @davegravy use the GDD tracker as a guideline. I have pushed my timing before and didn't experience excessive growth. Let it get to 100% and check your grass. Depending on your rates, your suppression might last longer than the tracker suggests.


I thought different rates gave different levels of suppression over length of suppression. Is that not correct?


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## Harts (May 14, 2018)

bhutchinson87 said:


> Harts said:
> 
> 
> > @davegravy use the GDD tracker as a guideline. I have pushed my timing before and didn't experience excessive growth. Let it get to 100% and check your grass. Depending on your rates, your suppression might last longer than the tracker suggests.
> ...


I believe suppression is suppression. Higher rate would produce longer suppression. Not more suppression. You can't over wet something, it's either wet or it isn't.....you can't over suppress grass is how I've perceived it. Maybe I'm wrong.


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## ScottW (Sep 16, 2019)

bhutchinson87 said:


> I thought different rates gave different levels of suppression over length of suppression. Is that not correct?


The reality of inhibiting a biochemical pathway is that it's probably both. Heavier app would mean more inhibition of gibberellic acid synthesis provided that a lighter app isn't already at a saturating level. There must be some logic to why the experienced users recommend to step up your PGRs to the effect you want rather than going all-in with app #1.
Heavier app would also mean a bit more product lingering after X number of half-lives, which could slightly extend the duration that you get Y level of suppression.
You'd also have to consider that gibberellic acid precursors are probably accumulating somewhere earlier in the synthesis pathway than what you're inhibiting. This is the foot on the gas pedal; the PGR is the brakes. Once the brakes are gone, you could get a surge of gibberellic acid and rebound growth.

The GDD model on greenkeeper had a target of 287 for my first app of T-NEX at 0.3 oz/M. This is on TTTF by the way. Qualitatively, I noticed "some" growth suppression but not a great deal.
Working up to 0.5 oz/M, the GDD model now has the target at 317. Qualitatively, there is clearly "more" suppression than I saw at the 0.3 oz rate. Not taking off as much with each mow at the same frequency.
The target difference of 30 GDD in this weather is about a 1.5 day longer interval. In earlier spring (cooler temps) that might stretch to a 2-3 day difference.
This is my first year using PGR. I'm not measuring clipping yields and I don't have control plots to make this scientific.


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## g-man (Jun 15, 2017)

@Harts the study by UNL showed that increasing rate increases suppression, but the GDD threshold barely changes. So your reapplication interval is mostly based on temperatures and not on rate.


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## davegravy (Jul 25, 2019)

g-man said:


> @Harts the study by UNL showed that increasing rate increases suppression, but the GDD threshold barely changes. So your reapplication interval is mostly based on temperatures and not on rate.


That was my takeaway from the study too. Thanks for confirming.


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## Babameca (Jul 29, 2019)

@g-man My PGR is above the GDD limit but the app is still showing 25% suppression (max was 37). Any idea why? It slowly trickles down the suppression, but did not kind of cut off. I did not see surge yet in my yard, but weather is weird that I can't be very scientific on this.


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## g-man (Jun 15, 2017)

Gdd threshold does not mean rebound point. I think I explained it in this thread. https://thelawnforum.com/viewtopic.php?f=9&t=533


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## davegravy (Jul 25, 2019)

I'm seeing my first app's estimated suppression fall (it's still >0%) and my new application rise at about the same rate. The net suppression has been about 32% each day. Curious if the first application will fall below zero at some point, or will just asymptotically descend to 0.


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## synergy0852 (Jun 30, 2018)

Your first application will eventually switch over to a % of rebound on Greeskeeperapp if I remember correctly.


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## Babameca (Jul 29, 2019)

g-man said:


> Gdd threshold does not mean rebound point. I think I explained it in this thread. https://thelawnforum.com/viewtopic.php?f=9&t=533


Thanks! At this point I was riding motorcycles :lol: Not even a forum member... :?


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## crstude (Jun 21, 2019)

Question- typically i hang in the warm season side having a mostly bermuda lawn. However, i seeded the north side of my house with TTTF and is shaded through the day that the bermuda (weed to you cool folks) wont move into. Anyways, with the raging summer heat starting, can I also apply pgr to help with the summer stress on the fescue, or is that a bad idea considering it was just seeded this spring. I've mowed it a couple times around 3" or so. Thanks for all the help!


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## Babameca (Jul 29, 2019)

@crstude If your Fescue has never seen PGR, I would pass at this point. It is an additional stress. If you have been applying on it since spring, then there are 2 camps (as per I've read so far). PGR helps with summer stress, but when application started at the beginning of the season Yes.


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## crstude (Jun 21, 2019)

@Babameca , thanks for the info. I have not applied any PGR thus far to the fescue, only the bermuda. I'll just have to keep up with the watering on the TTTF. Thanks again!


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## shadowlawnjutsu (Jun 9, 2020)

davegravy said:


> I'm seeing my first app's estimated suppression fall (it's still >0%) and my new application rise at about the same rate. The net suppression has been about 32% each day. Curious if the first application will fall below zero at some point, or will just asymptotically descend to 0.


Sorry for hi jacking the thread. But do you have to upgrade to premium to get that feature?


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## Harts (May 14, 2018)

shadowlawnjutsu said:


> davegravy said:
> 
> 
> > I'm seeing my first app's estimated suppression fall (it's still >0%) and my new application rise at about the same rate. The net suppression has been about 32% each day. Curious if the first application will fall below zero at some point, or will just asymptotically descend to 0.
> ...


You can track GDD for PGR for free. You do not need to upgrade.


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## crstude (Jun 21, 2019)

I guess I'm confused on what clipping yield suppression is. My GDD tracker is showing 105% suppression. What does that mean?


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## davegravy (Jul 25, 2019)

crstude said:


> I guess I'm confused on what clipping yield suppression is. My GDD tracker is showing 105% suppression. What does that mean?


Your grass is growing backwards lol 😛

Also curious to know what this value represents.


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## jhealy748 (Jul 25, 2019)

Thats weird mine has never shown much past about 37% suppression! Not sure I have an answer but am curious what others that use this have to say about this.


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## Spammage (Apr 30, 2017)

Mine is currently showing 42% suppression, applied on the same day. Why did you change the GDD reapplication timing to 200 GDD?

edit - if you are applying full doses more frequently than required, the suppression may be getting added together, meaning your past apps are still suppressing the growth along with the most recent app.


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## davegravy (Jul 25, 2019)

jhealy748 said:


> Thats weird mine has never shown much past about 37% suppression! Not sure I have an answer but am curious what others that use this have to say about this.


Same here, 35-40 max. If I do multiple apps I get a new progress bar for each, they don't add together


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## Redtwin (Feb 9, 2019)

davegravy said:


> jhealy748 said:
> 
> 
> > Thats weird mine has never shown much past about 37% suppression! Not sure I have an answer but am curious what others that use this have to say about this.
> ...


Yep, same here. I wish it would show the suppression rate for stacking. Mine will max out around 75% suppression but starts over at 0% each time I reapply.


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## crstude (Jun 21, 2019)

Spammage said:


> Mine is currently showing 42% suppression, applied on the same day. Why did you change the GDD reapplication timing to 200 GDD?
> 
> edit - if you are applying full doses more frequently than required, the suppression may be getting added together, meaning your past apps are still suppressing the growth along with the most recent app.


I changed the GDD to 200 from the default 225 as I noticed going from mowing every 5-6 days at .5" back to 2 or 3 almost to where there was no regulation. I wanted to be ahead of any potential rebound. It's been hot as hell too, and want to ensure it stays in regulation.


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## JRS 9572 (May 28, 2018)

This is what I've got. 2nd app. It says it will last until the 15th. But it hasn't figured in it being 97 today and probably that hot again tomorrow.


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## Redtwin (Feb 9, 2019)

JRS 9572 said:


> This is what I've got. 2nd app. It says it will last until the 15th. But it hasn't figured in it being 97 today and probably that hot again tomorrow.


It will recompute after each day so if you have a string of super-hot days, the reapplication date will get shorter.


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