I have grass that thus far is uncontrollable. It’s taken over almost half of my yard. I took some to a nursery and they said it was a species of johnson grass. Only grows about 1 foot tall and is very tough with a narrow leaf. What can I use on this that will not kill my St Augustine? Is there a preemerge and is it too late to use a preemerge?
Johnsongrass is one of the tougher weeds to control – especially when trying to treat a St. Augustine lawn. Over the years we’ve had people use two approaches. The first method is for when you have current infestations and involves the use of a post emerge.
Though the label does not list Johnsongrass specifically, we have had people apply both IMAGE and ATRAZINE to defeat it after finding it growing in their grass. This approach will usually require more than one application so plan on treating twice with the followup to be done 2 weeks after the initial. Also, target the Johsongrass. In other words, don’t spray the entire yard. And don’t soak it heavily either. Lightly spraying as much of the unwanted johnsongrass will do the trick if you treat throughout the season after it’s been growing.
The second approach is by far the most effective. Since johnsongrass comes back annually via seeds, a good application of a pre emerge like SURFLAN or RONSTAR G can keep it from ever growing. This is definitely the way to go. And there really isn’t a “wrong” time to use either. Both products can last 3-6 months so you need to be using it sometime in May-June then again in Sept-Oct and then again in Jan-Feb. I use it 3 times a year in my yard and have had great success keeping most any unwanted weed from growing. And the bottom line is it’s much easier to deal with these things with pre emerge products instead of a post emerge.
Here are direct links to the information and products listed above: