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Topic: Diluted strength of a weed killer ?  (Read 671 times)

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Offline Torment

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Diluted strength of a weed killer ?
« on: September 14, 2019, 03:13:52 AM »

Hello,

The consensus of an effective and strong weed killer appears to be Glyphosate 360 Concentrate, of which is 360 grams/litre

Mixing directions state:
24ml diluted in 1 litre of Water.

Therefore, what would be the final strength of such a dilution?

Thus, how much of the Glyphosate 360 is contained within the mixed Solution once diluted ?

I’m of the understanding that 360g/litre relates to its strength and if only 24ml is used and diluted with 1 litre of water, the final mix will not be as strong as implied.

In comparison, 1 litre sized Ready to Use Weed Killers, (which require no mixing) tend to state the active ingredient (Glyphosate) as being of 7.5g/litre.

I’m wondering; that once the Glyphosate 360 Concentrate is mixed as directed, will the final strength of the mixed solution be close to the 7.5g/litre of the Ready To Use Weed Killers ?


Prior to posting here, I did search the web for dilution formulas, of which and when found, were way beyond my level of understanding, although my search did lead me to this forum.

I’ll be grateful for an answer to my question.

Thanks

Offline Borek

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Re: Diluted strength of a weed killer ?
« Reply #1 on: September 15, 2019, 03:28:15 AM »
I’m wondering; that once the Glyphosate 360 Concentrate is mixed as directed, will the final strength of the mixed solution be close to the 7.5g/litre of the Ready To Use Weed Killers ?

Even a bit more.

Think about it this way - if there is 360 g per 1 litre, how much is in 0.024 L (that's what 24 mL is)?
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Offline Torment

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Re: Diluted strength of a weed killer ?
« Reply #2 on: September 15, 2019, 06:26:20 AM »

Exactly; it’s such a conclusion as to why I raised my question.

One litre of Glyphosate 360 Concentrate is 3 maybe 4 times more expensive than 1 litre of the Ready to Use/pre mixed Weed Killer.

 It’s implied that the 360 Concentrate is stronger due to being 360g/l; when in fact, it’s more expensive, as when the whole litre of the concentrate is diluted it can be sprayed over a much larger area than that of the 1 litre bottle of the Ready to Use Weed killer, hence the price difference but it’s not actually stronger.

Although this theory contradicts the various opinions and reviews  found online.

I’ve applied these Ready to Use 7.5g/l Weed Killers at appropriate times of the year but with very little effect, hence why I’m looking for a stronger /industrial strength Weed Killer.

Various online opinions state not to use more than the stated 24ml; thinking more will make a stronger solution when in fact it won’t

However, the more I think about it, the more confusing and contradictory it all is but thanks for your reply, much appreciated.






Offline Torment

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Re: Diluted strength of a weed killer ?
« Reply #3 on: September 15, 2019, 08:37:38 AM »
To clarify; I’m looking to compare the diluted strength of the Glyphosate 360 once diluted.

Currently, it’s looking that when the Concentrate is diluted, it has a far weaker Glyphosate content than the Ready to Use Weed Killer; although it’s implied and believed, that the Glyphosate 360 Concentrate is an industrial strength Weed Killer.

Ready to use Weed Killer; the Glyphosate content is stated as 7.5g/litre

Glyphosate 360 Concentrate = 360g/litre, although when diluted; 24ml is added to 1 litre of water; therefore, how can such a measure (24ml) be converted to gram/litre; so I can compare the mixed diluted strength of Glyphosate Concentrate with that of the Ready to Use Weed Killer ?

Would I divide the 1 litre Concentrate by 24ml; then divide that total by 360 ?

Such a calculation would equate to a Glyphosate content of 8.6 g/litre, which if correct, it’s beginning to make sense.

Offline Borek

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Re: Diluted strength of a weed killer ?
« Reply #4 on: September 15, 2019, 09:16:06 AM »
Would I divide the 1 litre Concentrate by 24ml; then divide that total by 360 ?

Honestly - not sure how you are calculating it, all these divisions should do not produce the correct result.

Quote
Such a calculation would equate to a Glyphosate content of 8.6 g/litre, which if correct, it’s beginning to make sense.

Surprisingly, that's what the correct result is (give or take).

If you take 24 mL of 360 g/L solution it contains 0.024L/1L×360 g=8.6 g, then you put it in a 1L, so the final solution has 8.6 g per L.

I don't have Roundup here at the moment, but I used it in the past. What I remember is that the booklet suggested different dilutions for different weeds. However, the strongest suggested solution was not enough for horsetail, I had to prepare an even stronger one (and it finally worked).
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Offline Torment

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Re: Diluted strength of a weed killer ?
« Reply #5 on: September 15, 2019, 05:36:44 PM »
Borek.. Thanks for your interest and replies to my post.

I’m by no means an avid gardener, although I wish to buy a more effective Weed Killer without paying more for a product believing it to be of an industrial strength when it isn’t.

It appears the Concentrate is only more expensive due to its quantity and when diluted, can treat a much wider area.

However, my Calculation to arrive at 8.6 grams/litre is as follows:

1000ml divide by 24ml = 41.66666666666667

360g/l divided by 41.66666666666667 = 8.639999993088

Which is approximately 8.6 and if correct; is only a little “stronger” than a Ready to Use Weed Killer?


According to Wikipedia; Glyphosate was brought to market under the trade name Roundup during the 1970s.

Offline Borek

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Re: Diluted strength of a weed killer ?
« Reply #6 on: September 15, 2019, 06:58:24 PM »
OK, by my book you made two mistakes that canceled out leaving you with a right answer.

1 L contains 360 g.

Obviously half a liter contains 0.5*360 g

One tenth of a liter contains 0.1*360 g

0.024 L contains 0.024*360 g=8.6 g, doesn't it?

You put 8.6 g into 1L, so the new concentration is 8.6 g/L.

If you were to put 8.6 g into half a liter, new concentration would be 8.6g/0.5L - 17.2 g/L.

And so on. Multiply volume by the concentration to find how much substance is in the solution, divide mass of the substance by the volume to find the concentration.

Which is approximately 8.6 and if correct; is only a little “stronger” than a Ready to Use Weed Killer?

Yes.

Looks like this document: http://www.herbiguide.com.au/Labels/GLY36_63078-0508.PDF contains some directions about preferred concentrations for different weeds. It is targeted for Australia, but should give you some idea about what concentrations are expected to be working. Looks like 8.6 g/L is quite strong.
« Last Edit: September 15, 2019, 07:09:56 PM by Borek »
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Offline Torment

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Re: Diluted strength of a weed killer ?
« Reply #7 on: September 16, 2019, 03:34:07 AM »
Borek.. Thank you for being good enough to explain and dedicating so much time to answering my questions.

Thanks also for providing the link explaining the Glyphosate dilution rates.

Unfortunately, although appreciated; your mathematical explanation is beginning to cause confusion.

If I understand correctly; despite the quantity, whether ½ a litre or 1 litre, the 360 content remains the same ?

I’m also finding it difficult to understand which substance is the Volume and which is the Mass ?


However, I’ve found this:
https://www.physiologyweb.com/calculators/dilution_calculator_mass_per_volume.html

Offline Borek

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Re: Diluted strength of a weed killer ?
« Reply #8 on: September 16, 2019, 05:49:18 AM »
If I understand correctly; despite the quantity, whether ½ a litre or 1 litre, the 360 content remains the same ?

Yes. Concentration is a quantity that doesn't depend on the amount of solution (we call these intensive properties), mass and volume depend on the amount (we call these extensive properties).

Quote
I’m also finding it difficult to understand which substance is the Volume and which is the Mass ?

Volume of the solution, mass of the solute (thing that is dissolved). Doesn't have to be this way always, but here it is.
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