Description of the issue:

no issue. just add the Herbicide Manual entry so you dont forget!

Is it still possible to make herbicide? Checking in JEI it doesn't seem to have a recipe.

Yep, the recipe got lost in transition to JSON recipes. This is fixed for future releases, but until then, you can use this datapack created by a community member to restore the recipe:

https://cdn.discordapp.com/attachments/270295745230405643/803190358572924938/Herbicide.zip