Ratio question


Well-Known Member
I have my sprayer calibrated at 15 gallons per acre. However, the speed I have to travel at to hit that mark is to fast for smaller plots. So if I slow down I know I will need more water to cover the entire plot. But at what point is to much water to much?
Look at the label on the specific herbicide you are spraying. Usually it will give you a range of volumes that are good to use. I'm out at the farm right now so can't look one up but I know from experience sometimes it will say "apply 2 quarts per acre mixing with a minimum of 8 gallons of water"
Can you reduce the pressure and then calibrate your sprayer again? Just watch your spray pattern when you do that, to make sure you get full width coverage at your desired height. That should reduce your water usage at a slower speed. Just reduce it by 10 psi max and try it. Like cutman suggests, the label will tell you what min and max water usage you can have. For glyphosate, it can range from 4-25 gallons/acre allowed.
I'll be spraying Gly.

I'll look at the label. Thanks for the idea about lowering the PSI I didn't think about that.
:) Not a problem. Just remember that if your plan is to put down 2 quarts of glyphosate/acre, for those smaller plots with less psi, and you use less water/acre, you'll need to adjust your mix.
Somewhere in all of this I admitted I spent a couple years running ag supply and agronomy centers. Let me just say some of the -- I want to call it crap but wont -- some of the spraying we did proved to me the rules aren't all that sensitive. Now, let me be quick to point out you should always follow the label instructions. That stuff they write is based on some pretty sound science, but it's also got a lot of "liability" coverage in it! If it doesn't work, you, the applicator, must be a real (insert not-so-good word here).

To the question. The amount of water you use is determined by your purpose. If you understand your purpose you will select the correct spray nozzle which gets you the correct gallonage, spray pattern, and droplet size. Not too many people here are applyig pre-emergent herbicides.This requires a different nozzle and amount of water, Flood jets produce "bombs" of water dropped on to the soil. The herbicide is part of the "bubble bomb" designed to get good soil coverage.

Most of what WE are doing is post emergent spraying. We need good leaf coverge - not soil coverage. And we choose flat fan nozzles. If there's a lot of vegetation to cover, you're going to need more water than if the weed bed is sparse. Let's make-up a rule. Suppose the rule says we will need 100 droplets of spray per square inch of target vegetation. It follows you need more carrier (water) for dense stands of vegetation. And, you'll probably want a little more pressure to create more mist.

But, like I said at the beginning, after you've thought about all the nitty-gritty at least once in your spraying career, you can pretty much go about your business as you see fit and be very successful.