Delete Older Backup History from msdb Database

-- Gets the oldest backup date in the backupset table
SELECT MIN(backup_finish_date)
FROM msdb.dbo.backupset

-- Gets the newest backup date in the backupset table
SELECT MAX(backup_finish_date)
FROM msdb.dbo.backupset

-- Purges the backupset table of all records BEFORE the one below in quotes
USE msdb;
GO
EXEC sp_delete_backuphistory '6/1/18';