This is a bit misleading, though my original post was a bit misleading too, now that I read it again (I was speaking more general, rather than just wheat, but may have misspoke regardless).

Glyphosate famously breaks down after two weeks, but those are for the perfect conditions, and the advice is to increase water to disperse the chemical. Textbook half-life is between 3 days and 19 weeks, though under what conditions, they are a bit hazy. Still, I would be inclined to believe that number when it comes to wheat.

Glyphosate on other crops, particularly trees for example, can take much, much longer to disappear, if at all. Trees that were sprayed 12 years prior can still have glyphosate in their tissues (Canadian study). Root plants are particularly good at retaining and accumulating it.