reclaimed field
畬 centers on land that has been cleared or worked for cultivation: a reclaimed field, typically after slash-and-burn or other preparation.
畬 combines 余 (possibly phonetic) with 田 (field), suggesting a field that has been worked or reclaimed. The exact historical development is uncertain.
The top 余 can be thought of as surplus or extra, and the bottom 田 is a field. Imagine taking surplus land and turning it into a reclaimed field ready for planting.
For ヨ, picture a yo-yo being used to mark out the boundaries of a reclaimed field: yo-yo -> ヨ, and the field is ready.