Wormwood is a plant that is very bitter and unpleasant to eat. This phrase describes the punishment that Yahweh was going to bring about on the evil prophets. In the same way wormwood was bitter and the water was poisonous, so would Yaweh's judgment be on the evil prophets. (See: [[rc://en/ta/man/jit/figs-metaphor]])
Here the evil teaching of the priests and false prophets is spoken of as if it were something filthy that ruined the land. Alternate translation: "evil has come from the prophets" (See: [[rc://en/ta/man/jit/figs-metaphor]])