Yes - it is an annual and redder and fleshier than panicum effusum. As you only have a few plants I would pull them out immediately - I suspect it is transported by mowers was it in the mown or unsown section of Bass Gardens?
Thanks Michael. I'll pull them out now. I hope not many seeds have dispersed. The plants I've seen are in the Conservation Zone but now that I'm sure about the id I'll look all around the park.