XL 2G Granules are safe to use on tall fescue and warm season grasses such as bahiagrass, bermudagrass, buffalograss, centipedegrass, St Augustinegrass and zoysiagrass.
XL 2G Granules - 50 lb. bag coverage varies on the application rate you are using. You will use 4.6 - 6.9 lbs. per 1,000 sq.ft. At most one bag will cover 11000 sq feet.
XL 2G Herbicide would be great to use as a pre-emergent weed control product. XL 2G does not control emerged weeds, established weeds, weeds growing from stolens, rhizomes, or root pieces. For the emerged weeds, you could use any glyphosate product, like GlyPhoSel Pro, to kill any and all weeds and grasses that might come up through the rocks. You can spray it as often as needed to get the control you need on the weeds you want to kill. Care should be taken to avoid spraying desirable plants as it will kill anything that it is applied to.
The product label (instructions) for XL 2G Granules can be found here: http://www.domyownpestcontrol.com/msds/xl%202g.pdf
Per the XL 2G product label, reseeding should be delayed by 8 weeks when using the 100 lb/acre rate or 12-16 weeks when using the 150 lb/acre.