There are many Piranha Creepers in this area. The Star is nearby, but it's blocked by a brick. Near the lone Flaptor is a plant with the first gem. Pull the handle in the sand in the corner to make a cannon appear. Use it to defeat the Piranha Creepers and Flaptors, and get the second gem. Also make sure to break the brick near the Star. Near where you start and go behind the wall to find a purple pipe. It leads to an area with a moving plant. Pick it to get the third gem. Return through the pipe and get the Star.
Special Challenge: Clear the course in one shot.
This means only firing one turnip from the cannon. Just aim at the brick in front of the Star.