# Does PreM Affect KBG Spreading?



## jaygrizzle (Jun 6, 2018)

I was just thinking about this and was unable to find a definitive answer. If I apply Barricade or Dimension would this slow down or prevent KBG from spreading?


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## probasestealer (Apr 19, 2018)

@ken-n-nancy answer takes the cake.


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

The short answer is that yes, application of pre-emergents slows down the rhizome growth of Kentucky Bluegrass. More pre-emergent is not better.

You want to apply the minimum pre-emergent to get the protection you need against whatever weeds make you decide to apply a pre-emergent, whether crabgrass, or _poa annua_, or ???

Don't just take my word for it, though. There are lots of studies on this topic. Below is one from CalState/UMass quite a few years ago. (Warning, this isn't an easy read, but there are some excellent charts at the end which show how the pre-emergents reduce tillers and rhizomes, and that the effect increases with the more of the pre-emergent that is applied.)

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.553.3928&rep=rep1&type=pdf

Accordingly, I make multiple lower-rate pre-emergent treatments (i.e. two 3-month rate treatments after one another, rather than a single 6-month treatment), as I think the grass tolerates the multiple smaller treatments better than single larger applications. (This is kind of the "spoon-feeding" mentality, but for the pre-emergent, instead.)

Some conclusions I would make include:

Don't apply pre-emergents if there isn't a weed you're trying to prevent

If there is a weed you're trying to prevent, a pre-emergent can prevent that weed for only a minor reduction in rhizome/tiller growth, if the pre-emergent is applied with a proper dosage.

Don't apply more of the pre-emergent than you need to get a level of control that is sufficient for your needs.

Make multiple smaller applications of a pre-emergent, rather than a single larger application, in order to reduce the total amount of the pre-emergent used over time.


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## ABC123 (Jul 14, 2017)

Going into this fall with a Reno isn't there soil temp restrictions for how late one can apply.


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## Sinclair (Jul 25, 2017)

ABC123 said:


> Going into this fall with a Reno isn't there soil temp restrictions for how late one can apply.


"Not frozen" is pretty much the only restriction.


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## jaygrizzle (Jun 6, 2018)

@ken-n-nancy thanks for the info. What I am trying to prevent is poa annua. I feel like I'm in a catch 22 where I have some bare spots that I want the KBG to spread and fill, but I also want to prevent poa a in the spring. So I'm torn about putting down fall preM.


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## FuzzeWuzze (Aug 25, 2017)

What does putting Fall Pre-Em have to do with preventing Poa in Spring?
Plenty of people put down Pre-Em every year that have all KBG lawns and they dont seem to complain about lack of spreading.


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

jaygrizzle said:


> @ken-n-nancy thanks for the info. What I am trying to prevent is poa annua. I feel like I'm in a catch 22 where I have some bare spots that I want the KBG to spread and fill, but I also want to prevent poa a in the spring. So I'm torn about putting down fall preM.


I think you're doing the right thing to be careful and prudent in determining how to proceed.

Basically, almost everything one puts on the lawn has advantages and disadvantages.

You have a known _poa annua_ problem. By applying a fall pre-emergent (in my area, I would have needed to apply that by now for _poa annua_, but maybe you're not too late yet in St. Louis, particularly with this hot summer potentially working in your favor), you will probably get say a 95% reduction in _poa annua_ germination, at a cost of maybe a 10% reduction in KBG spreading effectiveness.

If your _poa annua_ problem is about 1 _poa annua_ plant per ksqft, then you could probably just hand-pull those 3 plants out of your lawn. Accordingly, you wouldn't need to use a pre-emergent and could get 100% spreading effectiveness from your KBG.

If, however, you have about 1 _poa annua_ plant per square foot, then pulling 3000 of them by hand this fall isn't a good use of time. You're better off applying a pre-emergent to control 95% of that _poa annua_ (note, you'll still have about 150 to pull by hand...) and only getting 90% spreading effectiveness from your KBG.

Given that you have a _poa annua_ problem, you should definitely apply a pre-emergent, even though it will (slightly) reduce your KBG spreading, presuming that you choose a good dosage for a pre-emergent and apply it correctly.

Personally, I've applied a fall pre-emergent on my front lawn in two prior years to prevent _poa annua_ germination, and it made a big difference. The associated reduction in KBG spreading wasn't much -- the KBG still spread very well, especially coupled with aggressive fall fertilization.

I hope I didn't give the wrong impression with my earlier post. Your initial question didn't contain the full context, but just asked if Barricade (prodiamine) or Dimension (dithiopyr) would slow down KBG spreading. Well, the answer is, yes, it does. However, the reduction is small, if the pre-emergent is properly applied, while the benefit in _poa annua_ control is huge. The benefit greatly outweighs the cost, if you have a _poa annua_ issue.


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

FuzzeWuzze said:


> What does putting Fall Pre-Em have to do with preventing Poa in Spring?


Well, it depends up on which type of _poa_ you're trying to prevent. (You bumped into a personal pet peeve of mine to use "poa" as an abbreviation for _poa annua_, even though it is an abbreviation which is commonly used, but I digress.)

Presuming that you're referring to _poa annua_ (and not _poa trivialis_ which I can't stand in my lawn, or _poa pratensis_ which I am trying to encourage in my lawn), the _poa annua_ that us cool-season lawn folks see in our lawns in the early spring is mostly a "winter annual." It actually germinates in the fall, grows to a small plant before winter and overwinters as a small plant. In the spring, _poa annua_ is one of the first grasses to green up and grow. It quickly sets seed, even before some of the slower-to-green up grasses (like my Bewitched KBG) have really even greened up yet.

However, just to make our lives more difficult, _poa annua_ doesn't just germinate in the fall. More of it germinates in the spring, too.

Plus, _poa annua_ isn't strictly a "winter annual." A lot of it, particularly in highly-maintained (plenty of water, good soil) turf can survive the summer, making it a perennial in some places.

Furthermore, _poa annua_ doesn't produce seed at just one time of year, but can do so at basically any time the plant is growing, and it only takes about 6 weeks for _poa annua_ to go from just-germinated to producing seed in good growing conditions.

In any case, one of the best ways to reduce _poa annua_ in a lawn is by application of a fall pre-emergent to reduce the amount of _poa annua_ that germinates in the fall.

There's a lot of articles on the Internet about the _poa annua_ life cycle. One good one that I bumped into is https://www.extension.iastate.edu/turfgrass/blog/annual-bluegrass-poa-annua-control-so-where-do-we-stand-2014



FuzzeWuzze said:


> Plenty of people put down Pre-Em every year that have all KBG lawns and they dont seem to complain about lack of spreading.


Agreed. I'm one of those people.

The reduction in spreading from properly-applied pre-emergents is comparatively small (say 10-25%), while the benefit in control of undesirable weeds is 90% or greater. If one has a _poa annua_ problem, application of a fall-preemergent is definitely worth the minor reduction in KBG spreading.


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## jaygrizzle (Jun 6, 2018)

ken-n-nancy said:


> jaygrizzle said:
> 
> 
> > @ken-n-nancy thanks for the info. What I am trying to prevent is poa annua. I feel like I'm in a catch 22 where I have some bare spots that I want the KBG to spread and fill, but I also want to prevent poa a in the spring. So I'm torn about putting down fall preM.
> ...


Appreciate the further explanation. I remember seeing a bunch of poa A last spring which there was no way I could hand pull. So I think my answer is go with the fall preM to try and prevent it and just accept the possibility that the KBG doesn't spread at it's max potential.


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## Suburban Jungle Life (Mar 1, 2018)

I think poa a germinates when soil temps fall into the 70's. Maybe a target for applying prem.


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## jaygrizzle (Jun 6, 2018)

Suburban Jungle Life said:


> I think poa a germinates when soil temps fall into the 70's. Maybe a target for applying prem.


 I think I may go ahead and try and get some down today as soil temps will most likely be dropping soon. However, the forecast is showing heavy rain Thursday night - Satuday. Sounds like the potential for a few inches. Would this much rain be an issue to recently put down preM. At this point I'm going with a granular.


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## Green (Dec 24, 2017)

I accidentally put down pre-M meant for an area of a certain size on an area half that size. So, 5 lbs of Dimension instead of 2.5. Now, some people do use that rate. But I had really bad drought stress in that area compared to other years, with dormant patches, and possibly some dead grass. Connection? Maybe.


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## NewLawnJon (Aug 3, 2018)

I put down Dimension at the 3 month rate right before the soil temps hit 70 in my area, and have been spoon feeding .5 lbs of N/k every week and have been seeing a lot of my KBG spreading. I would guess that the two methods offset each other to an extent, but spoon feeding the lawn fertilizer and pre-emergent on a regular basis encourages spreading more than quarterly heavy doses.

I will need to put down Dimension at the 3 month rate again in October to cover me until the soil freezes, and hopefully get a little protection in case there are any warmer days in the winter, but spoon feeding the chemicals always seems to work better than heavy doses.


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