my only advice o nthe patches is to pull up the stuff growing in the patches, till it up a little and drop some sod in there. or just keep it tilled and in the spring time the grass runners will quickly fill in those spots..
st augustine seed is not available like bermuda seed is etc... at least it hasnt been in the past several years. so the only way to plant is sod or grass plugs.
i can tell you... on a fertilizer note. ive been using the Nitro-Phos brand of fertilizer and man that stuff works miracles! Ive been using that brand for about 7-8 years now and it always does a great job on our south texas st. augustine. first couple of mows in the springtime i bag the clippings so that all of that dead stuff from the winter is picked up. then every time after that i just let the mower mulch it and let it fall back onto the lawn to help give back nutrients etc. another thing i do is set the mower to the tallest setting and water every other day or so. my lawn is always thick and green! mowing the lawn very short often burns it in the summer and is not a good look. hehe. plus having the grass nice and thick helps to drown out those pesky dollar weeds. hehe
nitro-phos can be bought at houston garden centers
http://www.houstongardencenters.com/...e.php?idCat=45