Barley in Khrysalis has the highest level gardening spells like Ant Lion (which kills any level pests). In order to access the spells you have to complete a series of side quests that list completion of the Eclipse Towers as a prerequisite. You also have to be at least level 15 in gardening.
First you need to become a rank 15 gardener, then you will get a gardening quest in Bastion, Khrysalis. When you finish the quest, you will be able to buy the rank 7 pest spell from the gardener in Silent Market, Khrysalis.