Hi.. Thanks for the query.. Bitter taste in mouth can be due to causes like oral Infections and Infection on tongue, acid reflux, while the new herbicide that you are using can be a cause.. So my advise is to first of all take all necessary precautions and follow safety instructions before using pesticide. Also start gargling with flavoured mouthwash and chew flavoured sugarfree chewing gum.. You should avoid direct exposure to pesticide and always cover your mouth and nose.. Do warm saline gargles.. You can use a tongue scraper to clean your tongue as the particles can accumulate over tongue and cause bitterness.. Hope this helps.. Regards..