Paul wrote: ↑
August 1st, 2019, 11:40 am
Just a quick question Ken-n-Nancy from your post:
ken-n-nancy wrote: ↑
July 25th, 2019, 11:23 pm
oday we applied the first application of pre-emergent to stop Poa annua from germinating this fall: Prodiamine 65 WDG at a 3-month rate (0.5 Tbsp/ksqft).
From the label, the max rate for KBG is 0.55 ounces/1000 sqft per year. The rate you used was 0.5 Tbsp/1000 sqft or 0.25 ounces/1000 sqft. So does this mean you can only apply it two times per year before you hit your max rate?
Hmm. I know that I had previously determined that 3 applications of 0.5 Tbsp brought me exactly up to (but not over) the 0.55 oz/1,000 sq.ft. maximum. But your math seems right, too. So, where is the difference?
I used the "EQUIVALENT MEASUREMENTS For PRODIAMINE 65 WDG" table on page 4 of the Quali-Pro label which lists that 0.37 oz is the same as 1 Tablespoon and that 0.55 oz is the same as 1.5 Tablespoons. This table makes it pretty clear that 1.5 Tablespoons of product is 0.55oz of product.
What is going on is that the Quali-Pro label uses ounces of weight
while your conversion from 0.5 Tbsp to 0.25 (fluid) ounces is for volume
(liquid measure). It makes sense that the label is in weight, since the WDG pellets are in a dry form and are sold by weight (not volume) even though they are in a 5-pound jug (which sure looks like a jug for holding liquid!)
My hypothesis is borne out by the same table -- 1.5 lbs/acre = 0.55 oz/1,000 sqft = 1.5 Tbsp/1,000 sqft.
1.5 pounds is 24 ounces (weight). 24 ounces / 1 acre = 24 ounces / 43,560 sqft => 0.55 oz / 1,000 sqft.
So, to make the long story short, 3 applications of 0.5Tbsp/1000sqft of Quali-Pro Prodiamine 65 WDG totals to 1.5Tbsp/1,000sqft = 0.55oz/1,000sqft of product applied in a year, which is exactly the annual maximum listed on the label for Kentucky Bluegrass (no more, no less).
I make my three applications at (1) forsythia bloom which is around 25 April for me, (2) end of July, and (3) mid-September. This gives me pre-emergent coverage for just about the entire growing season in New Hampshire, with a weak spot in mid-July, and a bit extra coverage in mid-September. However, this approach provides the extra protection when I think I need it most -- in the peak of Poa annua
In any case, this whole confusion of ounces (weight) and fluid ounces (volume) is probably an example of why we should have all converted over to the metric system long ago...