if the barley is for malt, either dont do it, or get some very trustworthy and experienced  advice on timing.          Malt barley depends on  an undamaged germination, and  the dessicant product can  very easily do that...hence the advice not to use it as seed.

What reason do you have for wanting to do it anway..? 

It isnt unheard of, but it isnt the normal practice, and is quite likely illegal anyway, if not specifically covered on the chemical label.  If you did it illegally, then  you may open yourself to a dangerous situation as far as any sort of liability goes.