The Wishsong Of Shannara

Description for THE WISHSONG OF SHANNARA by Terry Brooks:

Horror stalked the Four Lands as the Ildatch, ancient source of evil, stirred to new life, sending its ghastly Mord Wraiths to destroy Mankind.

To win through the vile growth that protected the Ildatch, the Druid Allanon needed Brin Ohmsford -- for she alone held the magic power of the wishsong, which could make plants bloom instantly or turn trees from green to autumn gold. Reluctantly Brin joined the Druid on his perilous journey. Then Brin's younger brother Jair learned from the mysterious King of the Silver River that Brin was doomed - unless Jair could reach her in time!

So Jair set out through the very heart of evil. And ahead, the Ildatch waited, nursing its plans to trap Brin into a fate far more horrible than death!

This is #3 in Sword Of Shannara Series.