To enable alerts for Web application we use below code
$SPwebapp=Get-SPWebApplication "http://SharePointSite.com"$SPwebapp.AlertsEnabled = $true$SPwebapp.Update()# To Disable alerts for a Web application$SPwebapp.AlertsEnabled = $false$SPwebapp.Update
$SPwebapp=Get-SPWebApplication "http://SharePointSite.com"
$SPwebapp.AlertsEnabled = $true
$SPwebapp.Update()
# To Disable alerts for a Web application
$SPwebapp.AlertsEnabled = $false
$SPwebapp.Update