When should I use Preem on strawberries or roses?

I,m new at strawberries and roses and any help would be appreciated. I live in zone (6). I have several types of roses


and have june and everbearing strawberries.

When should I use Preem on strawberries or roses?
I'm not sure what Preem is...but if you are referring to the pre-emergent Preen......you will want to put it down early. It's a pre-emergent, therefore it stops the weeds from even coming up. If you have weeds already, pull the weeds and then put the preen down. Preen will do nothing for weeds that are already growing. I would like to know what Preem is if you aren't referring to Preen. I've just never heard of Preem.