Which one are you applying? The label should tell you when to apply it, usually it goes by soil temp (5 day average). Prodiamine can be applied early even in cold weather, as long as it's above 32f when you are spraying it. Cold weather slows down the rate at which it breaks down.

 

There's not a definitive window that it has to be down as it's more of a guideline but if the forsythia has bloomed then it's time to apply.

 

General rule is as the soil temp is reaching 55F. Also look at your long range forecast to make sure the temps are staying consistent.

Sometimes we get unseasonably warm temps for a few days and the plants and shrubs start to bloom but then a cold streak hits and everything grinds to a halt.

When in doubt, earlier is always better than later.

 

Which one are you applying? The label should tell you when to apply it, usually it goes by soil temp (5 day average). Prodiamine can be applied early even in cold weather, as long as it's above 32f when you are spraying it. Cold weather slows down the rate at which it breaks down.

The prodiamine jug that I have for dissolving in water has a map with dates, so I concur with this sentiment that the label should be your guide, basically, May 30th is the generic late date to apply in the north. The further north you go that date could be even later that's why temps and natural indicators like others have mentioned (forsythia) are used as a guide. As far as a window goes some published data says you can do a second app when soil temps are up to 65-70 degrees, I say the second app because generally, we apply at or before 55-degree soil temps for the first app of the year.

Others have had some prodiamine talk here: https://thelawnforum.com/viewtopic.php?t=15226

 

As soon as you can as long as the ground isnt frozen or saturated with water after a big rain storm.

 

Which one are you applying? The label should tell you when to apply it, usually it goes by soil temp (5 day average). Prodiamine can be applied early even in cold weather, as long as it's above 32f when you are spraying it. Cold weather slows down the rate at which it breaks down.

The prodiamine jug that I have for dissolving in water has a map with dates, so I concur with this sentiment that the label should be your guide, basically, May 30th is the generic late date to apply in the north. The further north you go that date could be even later that's why temps and natural indicators like others have mentioned (forsythia) are used as a guide. As far as a window goes some published data says you can do a second app when soil temps are up to 65-70 degrees, I say the second app because generally, we apply at or before 55-degree soil temps for the first app of the year.

Others have had some prodiamine talk here: https://thelawnforum.com/viewtopic.php?t=15226

The map in the label is for Germination and not for Application. MSU GDD tracker is a great way to know when to apply. 30may is likely too late except for Newfoundland, Canada.

 

+1 for the MSU GDD tracker. For a soil temp approach the GreenCast soil tracker tool is good: https://www.greencastonline.com/tools/soil-temperature

Although you'll want to apply at 55 degrees (or whatever your target temp is) in your area, use this as a guide and keep in mind that the areas near pavement heat up quicker. A meat thermometer works well for checking those areas. Apply when those areas are hitting your target temp.

 

I basically use the forsythia of when they start to drop or this year I'm probably gonna do it when they're in full bloom. (They're starting to show some yellow now).

 

Having a specific "window" is a myth.
You can put it down anytime, no window will stop you from this.

Categorize undesirables by germination temperature.
Youll find that they range throughout the year.

 

Having a specific "window" is a myth.
You can put it down anytime, no window will stop you from this.

Categorize undesirables by germination temperature.
Youll find that they range throughout the year.

This is incorrect. A window of application is not a myth. The MSU tracker is base on the research that if you apply too late, the plants might be mature enough to survive the prem.

 

A year round coverage is ideal. I do one in late fall that will cover me till april, most years ill apply it as soon as i can stick a shovel all the way down into the soil.

during the growing season ill do more frequent low dose applications

 

Having a specific "window" is a myth.
You can put it down anytime, no window will stop you from this.

Categorize undesirables by germination temperature.
Youll find that they range throughout the year.

This is incorrect. A window of application is not a myth. The MSU tracker is base on the research that if you apply too late, the plants might be mature enough to survive the prem.

Too late or too early dont really matter as long as teh ground isnt frozen or saturated. I rather put it down too early than late and rather put it down late than never. Preventing some is better than not having any prevention.

 

Having a specific "window" is a myth.
You can put it down anytime, no window will stop you from this.

Categorize undesirables by germination temperature.
Youll find that they range throughout the year.

This is incorrect. A window of application is not a myth. The MSU tracker is base on the research that if you apply too late, the plants might be mature enough to survive the prem.

It's not a window. It's a Deadline.
If you miss the deadline for March/April weeds, that won't stop you from putting down from protecting for crabgrass.
Therefore :> not a window but a deadline for specific weeds.
Deadline dictated by temperature which aren't dates but events.

Also, it's myth because one can do anything they choose. One can choose to Prem in the middle of January on top of snow if one chooses.
The window is not physical.

 

Correct, the window is not physical. But it is theoretical and it does exist with regards to the weeds you are targeting.

Applying pre-em in June, doesn't offer any protection from weeds that germinate in April and May.

Applying a pre-em in July doesn't offer protection against crab grass, which will most likely start to pop up in June.

The point is, there becomes a point in time where a pre-em app won't help very much. Yes, some protection is better than none. But more protection is better than some. Therefore, follow the 55F guideline.

@Agiuliano10 If you applied a pre-em app within the next two weeks, that should give you good protection.

You can follow up with a 2nd application in 8-10 weeks, if you wish.

Just keep monitoring your own soil temps with a digital thermometer.

 

Having a specific "window" is a myth.
You can put it down anytime, no window will stop you from this.

Categorize undesirables by germination temperature.
Youll find that they range throughout the year.

This is incorrect. A window of application is not a myth. The MSU tracker is base on the research that if you apply too late, the plants might be mature enough to survive the prem.

It's not a window. It's a Deadline.
If you miss the deadline for March/April weeds, that won't stop you from putting down from protecting for crabgrass.
Therefore :> not a window but a deadline for specific weeds.
Deadline dictated by temperature which aren't dates but events.

Also, it's myth because one can do anything they choose. One can choose to Prem in the middle of January on top of snow if one chooses.
The window is not physical.

Crabgrass Preemergence Timer (GDD32)
At-a-Glance: Base Temperature: 32 degrees F, Target GDD Range: 250-500, Source: Calhoun - Michigan State University (2004)

The window is defined at a GDD from 250-500. It is not a deadline.

 

General rule is as the soil temp is reaching 55F. Also look at your long range forecast to make sure the temps are staying consistent.

Sometimes we get unseasonably warm temps for a few days and the plants and shrubs start to bloom but then a cold streak hits and everything grinds to a halt.

When in doubt, earlier is always better than later.

Appreciate all of the responses...I think this is what threw me off because we had some 60 and even 70 degree days and all of a sudden everything started to pop (including forsythia) so I got a little worried I missed it. But according to this feedback here I'll make sure to get it down this weekend and should be all good

 

Follow-up question; some folks in my area won't be getting their spring cleanup done until May. The 5 and 10 year averages have the soil temps into the 60's. Is an application at that time worth doing?

 

Follow-up question; some folks in my area won't be getting their spring cleanup done until May. The 5 and 10 year averages have the soil temps into the 60's. Is an application at that time worth doing?

Yes, an application of pre-emergent when soil temps reach 60°F is still beneficial in preventing summer weeds, including crabgrass. An article mentions that 80% of crabgrass germinate when soil temperatures are between 60°-70°F. Study has even shown that applications made as late as June 1st in Indiana will provide control in crabgrass, of course not as good as if applied within the optimum conditions.

If you are unable to apply pre-emergent during the optimum condition, consider using a pre-emergent that is also labeled to control crabgrass at the early stages. Or consider applying a mix of both pre-emergent and selective post emergent herbicide in this situation.

https://www.canr.msu.edu/news/cold-temperatures-extend-application-timing-for-crabgrass-preemergence-herbicides

https://turf.unl.edu/research/weeds/CombiningPreemergentHerbicidesTankMixturesSequentialApplicationsProvidesSeason-longCrabgrassControUpperMidwest.pdf