[chicob]

Just as a reference, the last time I used glyphosate the concentration was 15 L of concentrate (glyphosate 360 g/L) to 1000 L water. This is equivalent to 5,4 g/L. The study mentions two concentrations, 10 g/L and 5 g/L, so I think this is representative. Generally I would use more glyphosate, but now I usually mix it with oxyfluorfen in order to cope with glyphosate resistance and use less of each.

[bryanlarsen]

Representative if the bees are drinking straight from your sprayer, for multiple days in a row.

[chicob]

Actually, it's the other way around. My bad.

I misread the paper: it says 5 mg/L and 10 mg/L, which is a thousand times less concentrated than the prepared spray. At any rate, this is the environmental dosage the bees come in contact with, not the sprayer's concentration.

So I searched for the basis for those targets of 5 mg/L and 10 mg/L.

The article reads:

"Glyphosate concentrations were chosen to mimic environmental levels, which typically range between 1.4 and 7.6 mg/L".[original article]

The reference for this interval[1] makes reference to three other papers. One of these (from 1988) makes reference to another study on the "effects of a 2.2 L/ha Roundup application".[2] Another, from 1990, mentions an analysis of water residues "following application of ROUNDUP (2.0 kg/ha)"[3].

I have no idea what residues I'd find in my property, but the recommended dosage of concentrated product is still 2-4 L/ha. I am currently doing 3 L/ha.

Different brands of glyphosate concentrate usually have the same concentration, but this value might have changed after 30 years.

[1] http://jeb.biologists.org/content/217/19/3457?ijkey=7c53a3bc...

[2] https://link.springer.com/article/10.1007%2FBF01705439

[3] https://pubs.acs.org/doi/pdf/10.1021/jf00094a045