[social port]

I didn't use a traditional PreM earlier this year because I was expecting substantial disturbance to the soil surface this spring from adding a patio. Instead, I used mesotrione (Scott's starter fert with meso).

I'm due for another PreM now. I was going to use Dithiopyr, but here is the problem:
If I apply now, my coverage will end in July. That is too late for a second round of dithiopyr if I want to reseed in September.

The solution...possibly:

Use another round of meso and then use one app of Dithiopyr.
I could do

Dithiopyr now and meso in July ( but that would be adding starter fert in the middle of summer -bad-)

Meso with starter now and dipiothyr in late May (covering me until early September). The downside is the use of fertilizer just before summer, but that is better than mid summer. Right? Not to mention temperature precautions.
From my calculations, I will still be under yearly max use rates of meso if I apply now.

Input here?

 

[FlyMike]

Are you wanting to use dithiopyr because you want the post-emergent effect from it? If you haven't purchased a pre-emergent yet what about prodiamine to get the coverage length you need.

 

[social port]

No, Dithiopyr intended as a PreM. I'm controlling established weeds with weedBgone.

I have two bags of dithiopyr already.

 

[FlyMike]

Is it possible to do 2 applications at a lesser rate so that you can get the coverage length? Maybe a normal rate to start and then a lesser rate when it's time to reapply?
(These are somewhat questions instead of solutions. I'm not sure if it would work but would like to know for future reference)

 

[social port]

Yeah, I was wondering that as well. I like that solution the best, but I don't know if the product can be effectively used that way. I know of people splitting Prodiamine apps, but I'm not sure about dithiopyr.
I've been doing some searching online, but so far I'm still moving though the weeds. TheGrassFactor did a video on PreMs recently. That might be a good resource.

 

[Green]

All pre-Ms degrade over time, so its possible to do a lower rate of Dimension so it doesn't last as long. It's a bit of guesswork and estimation. Are you doing granular?

 

[social port]

All pre-Ms degrade over time, so its possible to do a lower rate of Dimension so it doesn't last as long. It's a bit of guesswork and estimation. Are you doing granular?

Yes, granular application.

It seems tricky because sufficient efficacy of the product seems bundled with the duration of the effect.
For example, if application were a matter of delivering the correct amount to achieve a desired effect, then determining the amount of product needed seems straightforward.
But with splitting applications with these PreMs, it seems as though one must correctly calculate so that effective dose and desired duration of effect are achieved.

 

[Green]

What's your product's percent AI?
What rate do you normally apply, and how long does it usually last?

From there, we can come up with a guesstimate based on our experience as to what rate you might try for a certain duration. The guide on the bag is only a very rough estimate for this...you really have to go by your experience.

For example, 3.5 lb/M of 0.167% Dimension applied in mid April tends to last me until the first or second week in August, at which point it seems to be totally gone, but starts to trail off a bit during the second half of July. So, 4 months coverage. Where I live, we typically don't apply any pre-M until April, ever, and we want it to last until mid August or so, because that's when we can start reseeding.

I'll wait for you to answer those questions. But, my hunch is, depending on your answers and product specs, 2 lb/M now, and again two months from now...(or alternately 4 lbs all at once now) would probably do what you want. That's assuming you're using a 0.15% AI product.

Because of that, my rule of thumb has been that each additional lb/M after the first 2 adds an additional month of coverage (for the 0.15% AI strength product). I've arrived at these numbers by starting with lower amounts in my beginning years, and working up one lb/M each year. Of course, it may vary by individual climate...more sunlight and water tend to break it down faster.

 

[social port]

What's your product's percent AI?

AI at 0.27%

What rate do you normally apply, and how long does it usually last?

First time dithiopyr user.

The guide on the bag is only a very rough estimate for this...you really have to go by your experience.

We won't be calculating under the best circumstances, it seems.

I was planning to put down about 72 pounds of the product over 17k Sq ft. That is on the higher end of the suggested application rates per the bag. That application would cover me for 3 months.

Where I live, we typically don't apply any pre-M until April, ever, and we want it to last until mid August or so, because that's when we can start reseeding.

An August reseeding would be iffy here. August is very, very hot. I would be OK for reseeding during the first weeks of September.

Assuming an application in the next several days, I would need five months of coverage. I wonder if we could simply divide by half, making one application effective for 2 1/2 months and the other application effective for 2 1/2 months, giving me five months of coverage, with the coverage ending right around mid September (or maybe even a little before)?

 

[Green]

I'm guessing by how you're talking that you've used Prodiamine in the past.

0.27% AI is very high for Dimension. Much higher than the typical concentration (0.15%). Sounds like you've got a golf course product with very small SGN. I've used 0.125%, 0.15%, and 0.167%, and am basing my recommendations for your 0.27% on calculations (simple proportion math) that give the equivalent amount of AI to what I've used in the past.

72 lbs over 17K is also a very high rate for your particular product. My gut feeling says, too high...even for 5 months. I think we're getting into 6+ month territory, potentially.

If you want 5 months of coverage, but want to almost guarantee that it breaks down by that time, I would drop no more than 2.75 lb/M of 0.27% AI product, in total.

Usually, split apps of dithiopyr hold up more robustly over time than single apps of the same total amount, because you're dropping a fresh batch partway through the time period. That could be bad in your case. It's not like Prodiamine that hangs on a long time, binded to the soil forever. But that doesn't mean you can drop high rates and still expect to seed, either.

Personally, I'd be willing to take a few weeds in the couple of weeks before I seed, and rest assured the barrier is degrading. If you have Tenacity or Scotts starter with Mesotrione to use at seeding time, it's not a big deal to have some weeds for a week or two.

Are you aerating and overseeding in mid September? If so, having a very small residual left is no big deal, because the aeration will break it up. It may seem I'm contradicting my paragraph above, but I'm not. There's always going to be a little left...you just want it to be low enough to not interfere with the seed. It's all about compromise. Personally, I wouldn't go over 2.75 lbs/M, but that's me, in my area, with my weather. In your case, there's a possibility it will last a few weeks less than in my area. But if I were a betting man, I'd be leaning on the side of a bit less, anyway.

Here, if we don't seed by the first week in September (for Fescue) that grass isn't fully mature by the time there's frost. But it makes no difference...principle is the same...you want to almost guarantee the pre-M is worn down to almost nothing by seeding time. I think we average in the low 80s for August...that doesn't mean it doesn't get higher, especially in the first half of the month. It can and does go above 95 in August...just not every single day.

This past year, I seeded on Sept 9th. My barrier ran out about a week before. I'm sure there was a tiny bit left...but aeration negated it.

 

[social port]

This is a lot of great information you give here, Green. Thanks for the feedback and problem-solving with me.

0.27% AI is very high for Dimension

Yes, based on my reading, I thought that the product would be considered highly concentrated for Dithiopyr.

72 lbs over 17K is also a very high rate for your particular product. My gut feeling says, too high...even for 5 months. I think we're getting into 6+ month territory, potentially.

I selected that rate for the payoff of increased range of target pests. I would be OK with a lower rate, but would lose some in breadth of coverage.
The troubling thing here is the discrepancy between your predicted window of coverage (5-6 months) and what is suggested on the label (3 months). I wonder if the label is written assuming a lower rate of application--which would, I'm assuming, translate into a shorter window of coverage. If so, it would have been helpful to know how substantially differences in the amount of AI applied can alter the duration of coverage.
If I could get 5 months of coverage with 72 pounds over 17k, then I would need to worry with splitting applications. Hmm...

Personally, I'd be willing to take a few weeds in the couple of weeks before I seed, and rest assured the barrier is degrading. If you have Tenacity or Scotts starter with Mesotrione to use at seeding time, it's not a big deal to have some weeds for a week or two.

That is a very good point; but it also spins on the question of when the window of coverage will end. If I can get 5 months of coverage at 2.75 lbs/M (your suggested rate), then there is no real worry for the period in between the end of coverage and the reseed period (probably less than a week). If the duration of coverage is only three months, then I would be looking at two or so months of no coverage.

Are you aerating and overseeding in mid September?

Definitely overseeding. Aeration is uncertain. I'll do my best to assess for compaction in August. I would be willing to do aeration anyway if I needed to weaken the preM.

So, it sounds like you think it is best to do one app at 2.75 lbs/M, and that would cover me for 5 months, give or take a week or two.
I could do that and forget about this split apps idea. Your point about split apps making a fall seeding dicier is compelling enough for me to eliminate the option.

I take it that you don't find the meso app followed by Dithiopyr app to be a good one because I would be risking fall reseeding due to the PreM still being too active?

 

[Green]

You're welcome.

Ok, here's the thing about the rates...

Take a look at this bag label for a typical Lesco 0.15% Dimension product: http://www.kellysolutions.com/erenewals/documentsubmit/KellyData%5CSC%5Cpesticide%5CProduct%20Label%5C10404%5C10404-86%5C10404-86_LESCO_DIMENSION_CRABGRASS_PRE_EM_+_FERT_19_0_7_080311_7_11_2012_11_31_27_AM.pdf

Notice how it recommends 3.82 lb/M of product for 3-4 month coverage. This wasn't the product I used, but the label was similar in terms of numbers to the one I used, and the percent AI is the same as what I prefer at 0.15, so it's a good stand-in. I tend to think in terms of 0.15% AI!

Last year ended up being pretty hot, which is taxing for the barrier.

I used Dimension in early to mid April...just about exactly a year ago. I used 0.167% AI at 3.5-3.6 lb/M. That's equivalent to 4 lb/M of 0.15%, or 2.16 lb/M of 0.27%. I didn't have any crabgrass in areas where I applied it, period. Just a little bit of spurge breakthrough around August and September near the pavement.

I overseeded starting in late August, and did it section by section. I raked well, so the barrier should have been gone, even if there was a bit left. But there probably wasn't much left. I did have an issue with one of the overseed areas, but I'm not sure why. I don't think it was the pre-M. The front yard overseed on Sept 9th was the last area done, and there were zero issues, in any case. I wouldn't expect any, since I aerated the front areas, anyway.

Pretty sure that barrier lasted me 4 months, give or take. That's what you'd expect from the label.

If you add 1 lb/M to the amount I used to add an additional month or so (make it 5 lb/M of 0.15% AI), and then calculate the equivalent for the 0.27 stuff, you get 2.78 lb/M. That's why I suggested 2.75 lb/M of 0.27% AI now. You might be able to get away with going very slightly higher, but who knows!

I take it that you don't find the meso app followed by Dithiopyr app to be a good one because I would be risking fall reseeding due to the PreM still being too active?

I'm not saying it's a bad idea. I'm actually using Tenacity right now for my first wave of pre-M, and will be following it with Dimension. However, I'm not expecting to do much overseeding this August/September. I'm actually spot seeding now, so I can't use Dimension yet. If you go this route, you'll just have to readjust your rates again. It can be done.

 

[social port]

@Green :thumbup:
Your line of reasoning makes a lot of sense to me. I'm going to follow your plan, but I do so, of course, knowing that this is a best estimate and therefore involves some risk.
Thanks again for the suggestions and help here. I know that thinking about the details in this plan isn't all that simple nor is it everyone's cup of tea. It's very good of you to assist, especially when you are having to make conversions due to different AI concentrations.

For anyone following this thread, my final plan is to use dithiopyr 0.27% at a rate of 2.75 lbs pounds of product per K (or M). I am not going to use Mesotrione now because Green clued me in on the duration of the effect of Dithiopyr. If I did use Meso now and Dithiopyr in a month, the Dithiopyr might still be too active when it is time to overseed. I don't want to risk a non-productive overseed this fall because I have a lot of lawn to repair. You can see how this plan works out for me here
https://thelawnforum.com/viewtopic.php?f=9&t=1935 as the season progresses.

Thanks to everyone for their contributions!
'

 

[Green]

@social port, you're welcome. The way I figured out what rates work for me was trial and error for about 5 years. I've stuck with the same basic product (granular Dimension) all that time. I've tried single apps, split apps, etc. I started out using much less (2.5 or 2.75 lb/M of 0.125% AI), and tried a little more the next year, and so-on. I was initially afraid of using too much, but it turns out I was nowhere close to doing that.

I hope it works well for you. You're going to want even coverage. It might be tricky with such a concentrated product, but it's even more important because of that.