Happy Friday everyone, I know this topic has been covered before but need some help calculating the per gallon rate for my backpack sprayer of Actara and Avaunt that I just got. My first spray will be at petal fall, the label on Actara calls for 4.5 to 5.5 oz. per acre, Avaunt label calls for 4.5 to 5.5 oz. per acre, thanks for your help, Chris.
I spay 100 gal/acre, so lets use that number. 5oz material/100 gal water= .05 oz/gal
I’m not quite sure how to convert .05 oz to something useful. Perhaps using a $20 kitchen quality digital scale with gram capability. .05 oz = 1.4 grams (better check my math!!). With farm use chemicals like these which only require a very small amount, a precise conversion to grams is better than trying to convert to a volume estimate like teaspoons (or fractions of a teaspoon)
Chris,
Blueberry’s conversion looks good to me. I might add 100 gal. per acre spray is generally considered more than a 2X concentrate spray for full sized peaches. This would mean you wouldn’t need to spray to the point of run-off for your smaller batch.
I also agree it gets pretty foggy to try to convert dry powders to volume. The old rule “a pint a pound the world around” doesn’t work w/ powders. They are considerably more “fluffy” than liquids.
A small digital scale isn’t too costly (about $25) and makes things considerably more accurate for smaller areas.
Olpea
I use a digital scale for all dry measurements but in pounds or ounces not grams. Its the best $20 I ever spent! I can be confident that my rates are exact and are within the range set on the label and should not harm myself or anyone else.
In the old days I used a hanging scale because digital scales were so expensive. You could get pretty close, but not perfect measurements. The ability to weigh something as small as a fraction of a gram with a digital scale is a big step in convenience and safety.
I find all of the rate per acre stuff confusing! Especially when I spray 50 gal/acre on the peaches and 100 gal/acre on the apples. These rates just seem to work out without a lot of sprayer calibration. I’m hoping to try some alternate row spraying on the apples since the trees are so small its easy for the spray directed at one row to get to the other row. Don’t believe that would work on the peaches since the rows are much further apart and the tree canopy is so dense compared with the apples
How much water per acre do you spray on your peaches/
Rick and Olpea, thanks for the replies, according to what I can find online, .05 oz./gallon = 0.0003906312 gallons, which equals 0.30000487572 teaspoons or roughly 1/3 of 1 teaspoon per gallon. Does that seem about right?
Just spoke to someone with Dupont who makes Avaunt and was told the only way to calculate the dosage correctly is to calculate the amount of water per acre that is put out by the backpack sprayer which I do not know how to do. Boy this is getting complicated.
Chris,
I understand how you arrived at those calculations, but unfortunately it doesn’t work that way.
Dry matter doesn’t weigh the same as liquid matter. When you mention teaspoons/tablespoons you are talking volume. Ounces really refers to weight. What is confusing is that ounces can refer to weight or volume (for liquid) since liquid has a stable weight per volume. For purists, even all liquid matter doesn’t have the same density (but for most practical purposes water based liquids are pretty close to the same density, unless they really have a lot of solids mixed in).
When the label gives the dosage in weight (like for dry pesticides) they intend for the measurement to be in weight (like ounces). Weight doesn’t convert to volume (i.e. ounces to teaspoons) unless one knows the specific conversion ratio. When the label gives the measurement of a liquid measurement (like pints/acre) then intend for the applicator to use volume measurements (like a measuring cup). Again, don’t confuse weight with volume. Fluid ounces only equal ounces when measuring fluids.
I happen to have a measuring cup which comes with a four jug box of Actara (since you probably bought one jug, you didn’t get the measuring cup). Many dry pesticides come with their own specific measuring cup, if you buy a box/case. I have plastic measuring cups for Delegate, Actara, Assail, etc.
I happen to use one of my dry measuring cups (an Actara cup) for measuring out liquid pesticides. I marked specific liquid measurements (with a permanent marker) on the side of the cup using a measuring cup measuring out water. According to that cup, about 13 ounces of liquid measurement (i.e. water) equals about 8 ounces of Actara according to the Actara markings on the side of the plastic cup. In other words if one were to measure out 26 tablespoons of Actara, it would only weigh 8 ounces.
If your conversion above is to put 1/3 of a teaspoon of Actara per gallon of water, that would be way too much.
I can understand your frustration in calculating how much your backpack sprayer sprays per acre, but it’s not as tough as it sounds. Go out and spray a normal sized fruit tree with water. Examine how much water you used for a normal spray job on the tree.
Then measure the radius of the tree to the drip line (as an example, lets assume a 7.5 feet radius). Remember the old formula pi R squared. That will give you the area of the tree you just treated (In this case about 175 sq. ft.) Divide that by the amount of gallons you used to give you the gallons per square foot. Multiply that times the amount of sq. ft. in an acre (43560 sq. ft) to give you the amount of gallons you are spraying per acre.
Let me put some possible numbers to it, so you can have a reference.
Lets assume it took you 1/2 gallon to spray your 15’ diameter tree. 0.5 gal. divided by 175 sq.ft. = 0.002857 gallons per square foot X 43560 sq. ft. in an acre = roughly 125 gallons per acre you are spraying.
I’ve been spraying 100 gallons per acre w/ my airblast sprayer for peaches. I changed some nozzles this winter (went to some lower volume air induction nozzles) so I will have to recalibrate this spring. Calibrating a big sprayer is done basically using the same calculations I outlined for you, only on a larger scale.
Once you figure out how much you are spraying per acre (of spray solution) you can then figure out how much chemical to put in your 4 gal. sprayer.
The basic problem is that the labeled rate for most dry “farm use” chemicals is stated in ounces (or pounds). An ounce is a measure of weight (except fluid ounces which is different) but a teaspoon is a measure of volume. Except for water where the density is known to be 1 gram per ML (density =1) it difficult to make an accurate conversion from weight to volume like ounces to teaspoons unless you know the density of the material. Sound like chemistry class?
The easy, fast and safe solution is to just weigh the material!
Fortunately the measuring device only cost about 20 bucks!. Once you try this process you will like it. It removes most of the confusion and the chance of making a big error when trying to convert a pesticide where the rate is given in ounces per acre (weight) into teaspoons or tablespoons (volume) per gallon. In the case where the rate is given in fluid ounces per acre, the teaspoon or fraction of a teaspoon should work fine.
Is a good rule of thumb for this to figure on 100 gal per acre?
I think 100 gal/acre is a reasonable number for the calculation unless the label says otherwise. In my case I spray 100 gallons on 600 apples which is 1 acre, (.167 gal/tree) but only 50 gallons on 120 peach tree which is also 1 acre (.41 gal/tree).
Hi Chris,
How did Actara and Avaunt work for you from a backpack sprayer? Did you get the spray amounts worked out?
Thanks,
Spud
Hi Spud, they both have worked great and I am glad I made the purchase. The are both a dry powder that mixes easy with water. From what I recall, I called the manufacturer on one of them and they could not give me a per gallon rate. The best I could come up after digging around online is a rate of 1/3 teaspoon per gallon which I have been using.
I like that the label on both does not require a respirator for use.
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Thanks for the update Chris. I have issues with plum curculio and stink bugs - do you have the same pests and did Avaunt and Actara work well on both insects?
Spud, I have not had a stink bug problem yet so can’t help you with that one but I no longer have a PC problem.
“A pint a pound the world around” Only works with water. It is the most ridiculous saying ever.
It doesn’t work with dry ingredients, it doesn’t work with alcohol, honey, motor oil, gasoline or anything.
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