Combining two herbicides

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Hi. If I have two different herbicides and one requires 2oz per 1 gallon water , the other requires 3oz per 1 gallon water do I put 2oz of first and 3 Oz of second into just 1 gallon water or 2 gallons of water. ? I'm taking guidance from University of Tennessee here for Poa Annua control, they recommended certain combinations but they said I need 4oz & 6oz of the two into two gallons. I disagree, hence my question.

https://youtu.be/O4sKzPLnoq4
 
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@Oliver Buckle that would dilute each by half. The correction would be cut the applied area by half to make up for it.

@DaveM The water is irrelevant so do not get mentally drowned by the gallons. It has a use as a dispersant medium and even a solvent, but it is more important to mark off an area and register (sight in your sprayer) such that you know how much liquid per square area your sprayer is throwing out. To many different pressures and orifices to bother telling anyone how their rig works. Then add to those variables a few more like the fast walkers, the slow walkers, machine pumps and so forth. Sorry, you gotta do you on this important detail.

Many times the area has to be backed out of the manufacturers label, which is the law and the ONLY formula you should be following, because I may have your product too but oops! they changed something recently!. The guys on the vid were talking pounds per acre on some products. Imperial units are a pain in the potato. Metric is so much easier because 1 mL water is also 1 gram of water. If i want to make a "gallon" of 1% solution in metric then I can easily say 4000mL water is 4 liters and also 4 Kg. Since 1% of 4000ml is 40ml I can pour 40g of water onto a scale from the metric "gallon" of 4 liters, then simply replace it with 40g of herbicide regardless if the herbicide mix has more or less volume than water due to the solids or other components of which it is made up..

If someone has calculated mixtures for their product but not your blend, you have to learn what the product mass to water mass ratio is so grams are helpful since they are a unit of mass. In imperial units this is called specific gravity. In metric it is the same idea really, its just that imperial units do not have some easy relationship to water that says 1 pound of water equals 1 quart or cup or something like that so metric is far easier.


The idea of how much mass of product per 1000 square feet is going down (or square meters) is the problem to be solved.

I hope this helps clarify your questions to yourself as well. The mixture mass is no less important than the quantity of mass questions related to the volume of spray medium water.

You may find it useful when adding a third component such as a spreader sticker or a soap or non-ionic surfactant.

One reason I hate the Oz measurement is fluid ounces vs pound ounces. I am like "Enough already"! Anyway buy a digital scale. Mine (OXO brand) was 11 bucks. You can check it for accuracy because now you know 250ml of water weighs 250g. Just remember most of the kitchen style measuring cups use the bottom of the meniscus, not the top, when measuring water. Some scales will pick that mass up. I use one that measures to 0.01g sometimes.

@Nasir your math in this area is better than most. What say ye?
 
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@Oliver Buckle that would dilute each by half. The correction would be cut the applied area by half to make up for it.
You are right, I should have said I would mix the appropriate amount for a gallon of each with half a gallon of water and then mixed them. Not sure about American gallons or 'metric' gallons, I know an imperial gallon as four and a half liters, actually a tad over, but only a tad.
Actually if someone said to me a mix of so much to the gallon I would assume the gallon included the product, put it in first, and then make it up with water so there would be that much in a gallon, a damn site easier than all that math, I must admit it confuses me, and as you say the water is irrelevant.
 
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You are right, I should have said I would mix the appropriate amount for a gallon of each with half a gallon of water and then mixed them. Not sure about American gallons or 'metric' gallons, I know an imperial gallon as four and a half liters, actually a tad over, but only a tad.
Actually if someone said to me a mix of so much to the gallon I would assume the gallon included the product, put it in first, and then make it up with water so there would be that much in a gallon, a damn site easier than all that math, I must admit it confuses me, and as you say the water is irrelevant.
As I have sprayed over years I see that weeds like wild violet and worse, like virginia buttonweed, have moved into the void. I have a rural yard with a pasture and forested area on two sides. Seed simply arrives. The cure seems to be ever nastier chemicals with ever smaller quantities needed at ever higher prices. Those stronger chemicals are real tree killers, like triclopyr and msm. I found myself holding back last year because of the risk. Its a bit agonizing because of the risk since it now time to spray but I really do not want to and the alternative is start over. The front yard is 20,000 square feet or so, about a half acre, and I do not want to buy sod or seed just to watch it go to weed again.
 
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Thank you so much, its complicated but I think you all are saying if the concentrate is 2oz (or whatever measurement) then it doesn't matter if you use 1 or 2 gallons water. What matters is how many Sq feet the label says per oz. For example Image herbicide is 2.5 oz per gallon from a bottle containing 32 oz to cover 8000 sq feet. So in this example there are 32/2.5 = 12.8 measures in the bottle. 8000/12.8 = 625 sq feet coverage per 2.5 oz concentrate "irrespective" of the number of gallons of water.

in my original example of two herbicides 2oz and 3oz then given they might have different coverage areas per oz the answer is to mix the 2oz first, calculate the coverage in sq feet (lets say 600 sq feet) , gallons of water doesn't matter, then for the 2nd do a reverse calculation starting with 600 sq feet and the result is how many oz to use for #2. This way we have the exact oz for an exact area, water doesn't matter, 1 gallon or 2 or whatever, I simply use the total gallons on the specified area.

am I correct ?
 
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Exactly so, it's a vicious circle, the more you use the more you need. I use physical attack, mostly a hoe when they are small, I don't know how you could manage that on your size plot, but though seed arrives surely it is possible to get a bit of ground reasonably clean by germinating and tilling? Then you have to plant so it establishes quickly and the weeds can't compete. I don't know your weeds of course, but over here they are things that clung on in marginal soil at the edges of forests until we cut down the trees and tilled the land, bonanza! But when they are young they are vulnerable.
 
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NEVER mix chemicals.
This is the best advice of all especially in the sense of chemicals to a specific purpose. The labels usually address this as a compatibility instruction. I mix different products such as a bug spray and a fertilizer but never two herbicides or two fertilizers etc. You may create and acid, a salt, a alkaline mix unintentionally for example. Herbicides for lawns are like chemo therapy chemistry in the idea that the toxic materials are less deadly to the grass type plant than the target. This is related to a variety of detail such as the speed at which weeds grow vs grass types and not so obviously the temperatures impact that type situation as temp changes speed of growth and thus the scenario where the weed is taking up more poison than the grass due to its higher growth rate. This is also related to the rate of decay of the herbicide. Its a mess when you combine things because of the highly specific designs in the chemistries.
 
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Bees, that is exactly what I was going to write! Zigs pointed out to me recently that I shouldn't be mixing two cleaners in the house as I was making chloro (something ) gas. :eek:
That brought back a memory, someone cleaned out the ammonia based footbath at a swimming pool where I worked with chlorine bleach, and we had to evacuate the entire pool for several hours because it produced clouds of chloramines.
\\\\\agree, generally not a good idea.
 

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