How to delete all webs and all there subwebs using powershell

I want to delete all webs and subwebs like this,

Add-PSSnapin Microsoft.SharePoint.Powershell

Get-SPWebApplication http://ift.tt/1Docp2s   | Get-SPSite -Limit All  | Get-SPWeb -Limit All | where {$_.Url -Match "crates"}  | ForEach-Object  {

        Remove-SPWeb $_ -Confirm:$false
}

How to delete subwebs and there webs here ?