In Secret Weapon, a convoy of Trooper Badniks led a weapon through the Zone but were ambushed by the Freedom Fighters. The weapon turned out to be Vermin the Cybernik who proved more than a match for Shortfuse the Cybernik. Fortunately, Amy Rose knew the geography of the Zone and used the acid from the Gum Tree Berries to defeat the villain.
Knuckles the Echidna has since visited the Zone and harvested a number of the berries to take back to the Floating Island. He would come to use the berry juice against a number of Badniks when he and the Chaotix Crew piloted the Floating Island in combat in The Battle For Mobius.