What is "very very quickly"?
From Wikipedia:
> The reported half-life of glyphosate in soil varies from two to 197 days with a typical field half-life of 47 days being suggested.[56] Soil and climate conditions affect glyphosate's persistence in soil. The median half-life of glyphosate in water varies from a few days to 91 days.[56] At a site in Texas, half-life was as little as three days. A site in Iowa had a half-life of 141.9 days.[94] The glyphosate metabolite AMPA has been found in Swedish forest soils up to two years after a glyphosate application.
It has a lower half-life in water, and a lower half-life when it's warmer. I store my oats both dry and cold.
As for cancer, I don't know - but it certainly is giving everyone parkinsons.
But you see - this is the whole problem. Every time I tried looking into it myself all I could find was that "dessicating crops with glyphosate is safe because it breaks down before it makes it into your food". If that is just simply not true or at the very least "true but only in ideal conditions that happen 5% of the time" then we're all screwed and no one seems to care.
> it certainly is giving everyone parkinsons.
That's a personal opinion. Actual scientific research is divided, and therefore anything but "certainly".