Do the math! 20 oz divided by 20 gallons(2560 oz.)= .78% solution, 20 oz. divided by 30 gallons(3840 oz.)= .52 % solution and so on. The more water you use the less % of glyphosate you will have. According to the instructions most plants require a 1.5 % solution to effectively kill them.
You are right but so am I. If I put 40 gallons water in my tank, and only 20 oz of 41% gly - and spray in second gear - then I have 20 gallons solution left after I spray one acre. And I would need to spray it all a second time - to get all 20oz down on the acre.Thatwouldbe the same as applying 20oz per 20 gallons (but with better coverage in the end).
I think I read 20oz/acre - but used 22oz - just because. Mixedin 20 gallons works well for me - but most of my spraying is done on plants 6" or less when applying to Roundup Corn/Soybeans - I've had some larger plants not die back 100%.
FH