On 17/06/2014 17:36, Tim Watts wrote:

My bottle is probably several times more
concentrated than the average garden centre stuff

Probably not. According to Wikipedia, the strongest available solution
contains 68% glyphosate (eg Bayer Super Strength Glyphosate, which is a
soluble granule). You can buy a 36% solution of glyphosate for garden
use in any garden centre.

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Jeff