schtasks doesn't allow tasks with wildcards AFAIK. You cannot disable an entire folder of tasks that way.
Option 1 is to first get all the tasks in the task path and then enumerate them one by one and call the command.
Option 2 is to use Powershell (PS 5+) that has cmdlets that can do this.
Get-ScheduledTask -TaskPath "\FolderBlah\" | Disable-ScheduledTask
Note that task paths must start and end with a slash.