You must read the label on pre-emergents with special note to make sure read what weeds that particular brand "gets". If a weed you particular want to get isn't on the list, in all likelihood that brand probably will be of little use. Please note these are pre-emergents. They work on killing weeds as they start germinating and useless against weeds that are already growing.
Also after a few years of using the same brand which "worked" but new varieties of weeds start taking over which are not being "killed" by the brand you have been using. Now without competion the "new" weeds take over. That is why every few years you have to change brands to get your new enemy weed (s).
We used Ronstar that worked to get perlwart (a moss like grower, which is strangely a member of the carnation family). And then a few years ago a new weed began taking over. It was identified as mossy pygmyweed, (strangely a member of the jade plant family which allows it to multiply quick both by the leaves rooting and the plentiful seed it produces). We have turned to Freehand which has been effective against the pgymyweed and every other weed that has been a problem here (for now).
