View Full Version : How do I figure out herbicide ratio/application?

May. 28, 2012, 07:37 PM
I've got a 15 gallon pull-behind tank with an 80" boom

I have 2+ gallons of Roundup Powermax.

The Roundup directions are telling me, I think, I need 44 ounces of that per acre for the height of weeds I have.

I'm doing my riding ring, about 100x200, so 1/2 acre-ish.

How does that translate to my 15 gallons of water? The Roundup instructions are terrible for folks like me LOL

May. 28, 2012, 08:59 PM
You need to figure out how much water your sprayer is calibrated to apply over an acre. Measure out a smaller test area that you can run over with your sprayer filled only with water so you can determine how much water is put out. In your test run, measure the length of your pass multiplied by the width of your boom in feet to get your approximate square footage of your test run. Divide the square footage of an acre (43,560) by the approximate square footage of your test run - then multiply that number by the number of gallons applied to find out how many gallons/acre your sprayer would have put out had you gone over the full acre. Then put the recommended amount of herbicide per acre in your tank along with the gallons of water you determined you'd need per acre. Fill partially with water, then add your herbicide, then finish filling to make sure it mixes evenly in your tank.

So say just for a rough example you measured off a 1/4 acre (10,890 sq ft) and found that your sprayer puts down 2 gallons of water over this area when travelling at a set speed. So this means that your sprayer would put down 8 gallons in an acre at the same speed... which means you need to put 44 ounces of herbicide per 8 gallons of water in order to get the correct application rate for the area you're treating.

Remember to keep your speed consistent between your test runs and your actual application or it will change your rate of application. You're going to need 22 ounces of herbicide for roughly 1/2 acre but you just need to determine the amount of water to put in your tank based on your calibration test. Hope that helps and makes sense! :winkgrin:

May. 28, 2012, 09:04 PM
OMG it really has to be that complicated?? Dayum! :lol:

Tamara in TN
May. 28, 2012, 09:06 PM
OMG it really has to be that complicated?? Dayum! :lol:

Skip is correct


May. 28, 2012, 09:09 PM
Well that's the *correct* way of doing it! haha! The other answer is fill 'er up, dump in your Roundup and take off driving. :lol: But in reality, once you do this one time, you should only need to do it once in a while as a recheck unless you modify your sprayer equipment or decide you want to drive faster when applying :D

May. 28, 2012, 09:10 PM

okfine, if you say so!

May. 29, 2012, 09:41 PM
Now, I am not exactly a tree hugger but RoundUp is getting more and more controversial. I do use it but sparingly and with thought. What is very effective and environmental friendly is “industrial” strength vinegar. IMO perfect for your ring. I haven’t check on prices recently but I would bet it should be competitive with roundup if not cheaper. Maybe a bit more but you would be doing the “right thing”. An internet search will give you the details. Even if you “over dose” no worries.

May. 29, 2012, 09:45 PM
gumtree, I agree, and trust me, in the 8 years we've lived here I've gone though a whole 2 gallon containers of Roundup which has been used specifically on poison ivy. Nothing else has had any chemical treatment, despite my sometimes-desire to napalm things ;) ;) :)

If I can get agreement with more people that full strength ACV would do the trick, I'd be all over it, but if it has to be full strength, it certainly won't be cheaper (which is not really the point, just commenting :))

With the last 2 years of very little riding and even less dragging, the weeds in there are simply out of control :( :(

May. 31, 2012, 08:16 AM
JB, I did a little research because I have only used vinegar in small spot sprayers. It seems it has its draw backs in large applications at this time. This is a pretty informative link, http://www.garden-counselor-lawn-care.com/vinegar-weed-killer.html
When we bought this farm the sand ring had not been used much and was far more green then white. Paid a local kid around $100 to hand weed the whole thing. He seemed pretty proud of his work when finished. Very tangible.

May. 31, 2012, 09:33 AM
I've hand weeded this ring twice - not doing it again LOLOL!

Thanks for the link - good reading.

May. 31, 2012, 11:12 AM
Just another case to prove it's important to pay attention in math class. :)

Jun. 1, 2012, 09:23 PM
Isn't there an "use this many oz of roundup per gallon of water" formula on the roundup? I'd just mix that concentration and spray until I'm done with the area - if I run out, mix some more; if any is left over, save until needed in the sprayer......


Jun. 1, 2012, 10:45 PM
Lorilu, I wish it was that simple :( All it says is how many ounces of Roundup per acre.

As stated, how fast you go has an immense bearing on how many ounces of the product get applied, regardless of the concentration of the chemical in the water.

40oz/gallon going 10mph will apply half the actual amount of chemical as 40oz/gallon going 5mph

I wish it had the conversion like that - to get 44oz/acre (which is what I need) then go X speed at 4oz/gallon, or something like that LOL

Jun. 1, 2012, 11:04 PM
I do that size arena with 32oz of 41% glyphosate in 50 galls of water. Just keep driving until it's empty.

There are many variables to bear in mind; speed, nozzles, pump, etc... Experience will be the only way to know what works best.