Main Walkthrough

Prerequisites: Complete A Plumbing Problem, repair the bridge to Barren Wasteland

Reward: Moon Cloves

Unlocks: --

In order to trigger this quest you need to bridge the gap to the Barren Wasteland. This requires Approval Badge 3, as well as completing the associated quest, A Plumbing Problem. You can then fix up the machine / bridge that will allow you to get into Barren Wasteland. This process costs 5,000 G, 2,000 Wood, and 1,575 Rocks, so you might be working on this last step for a while.

Approach the bench to the south of Willow Waters Bathhouse once you've unlocked the Barren Wasteland. You'll hit a cut scene with Rue and Xiao, and Rue, consulting a textbook, will ask if you've ever seen a Black Lotus before. You'll then be pointed to the south of Moonbury Island to find the Black Lotus, which is, coincidentally, the Barren Wasteland. 

Make a trip to the Heart of Barren Wasteland Fast Travel point, then follow the path south, east, south, and west. You'll wind up at a dead end with a bunch of flowers that aren't looking so great. Bubble will confirm that this is the Black Lotus, and the fungus surrounding the flowers is causing the trouble. You can solve the issue with a bit of research.

Use the Research Bench back at home - Wind is the far-left icon, Fire is the bottom-left icon, Earth is the center icon, and the bottom- and top-right icons are Water - to unlock the Fungi Duster. You'll need to craft this to get rid of the fungus. You can only use Water materials to complete this crafting project, so you'll need to get your Cauldron to at least the second upgrade level. 

Here are some ingredient suggestions for creating the Fungi Duster:
  • Place two Golden Shells on the left side of the template. Golden Shells are dropped by Goldenhorns, which are found in Glaze Iceberg and the Barren Wasteland.
  • Beneath the lower Golden Shell you can place a Feverfew. Feverfew is found in the northeast of Meadow Range.
  • Tucked up beside the lower Golden Shell and the Feverfew you'll find a spot for a Daisy. Daisies grow right at the entrance of Meadow Range.
  • Place a Rainbow Dew near the top-right of the template. Rainbow Dew is found in the south of Meadow Range, once you've completed Unknown Residue.
  • Some Luminous Crystals will fill the gap beside the Rainbow Dew. Luminous Crystals are dropped by the Koblin Mages of Barren Wasteland.
  • All this will leave a single in the top of the template. You can fill it with a Sour-Tasting Sap. Cut down the trees of Meadow Range or Glaze Iceberg to get some.

Take the resulting Fungi Duster to Bubble. She's almost always found at either the Ranger Station or Forrest's House, a short distance south of the Ranger Station. The two of you will head out to Barren Wasteland to get rid of the fungus, allowing you to harvest Black Fungus from now on. Slice up the three specimens that are here and take them to Rue for your reward. She wanders all over Moonbury, so you'll probably need to your dog to track her down.