Dragon Root is a plant that grows on the Isle of Berk It is the exact counterpart of Dragon nip, instead of making dragons calm, it makes them go crazy and attack each-other.
In Dragons:Defenders Of Berk Edit
In A Tale of Two Dragons, the riders were clearing Mildew's cabbage field when Hookfang and Stormfly started to fight. it was later discovered by Meatlug while she was digging in the field. When Hookfang and Stormfly started fighting again, Barf and Belch got to close to the root and started to act crazy as well. But eventually, every dragon was calm and Meatlug removed the root and tossed it into the sea.
Dragon Root looks like a cactus combined with a radish.
A Tale of Two Dragons