I also have a bermuda lawn which I feed organically, but do pre-emergents 3 to 4 times a year (at the lower recommended levels). I hate weeds. The greenlight you note has Dimension, which is the commercial name for Dithiopyr. Good stuff. I usually mix what i use for each application as they all have ceratin strengths and weaknesses. Barricade (Prodiamide), Dimension, XL2G (Benefin and Orzyalin), Team 2G (Benefin and Trifluralin), Gallery (isoxaben).

I used to get mine online through Pestrong and doyourownpestcontrol
http://www.pestrong.com/
http://www.domyownpestcontrol.com/?gclid=CLLe1IbRkrwCFUXZQgod-TAA5A

Expensive, but they do include shipping cost.

I now get mine through the local farmers coop and it is approx. half the price. Have to believe there is something like this in Central Arkansas or at least Little Rock.

Your cheaper alternative is Scott's Halts (Pendimethalin) through the big box stores. Much cheaper, but I do not beleive it is as effective over the long term.

Whichever way you go, remember for the spring application (or any for that matter) is timing and making sure it gets watered in either by rain or sprinkler.

One thing I forgot. Since your bermuda is probably dormant as mine is in middle TN, now is a good time to go out and spot treat anything green with Round-up. Hit them with a couple of squirts and then prowl again in a week or two for a second shot.

This should kill the weeds without affecting the bermuda since it is basically a sleep.

A healthy vigorous stand of turf grass will keep most of the poa anna out. First make sure that the weed is poa anna, and not a perennial cool season grass. Poa anna will not usually make it through the summer in your area. However, you must fix the underlying problems to keep the poa anna out of your yard. Does the bermuda get enough nitrogen fertilization at least a couple of pounds of nitrogen per 1000 square feet during the growing season. You said that the problem side of your yard has a lot of shade are tree roots also competing for water in this area? Also, bermuda grass needs at least 6 to 8 hours of direct sun a day. If that can not be achieved then maybe you need a more shade tolerant turf, such as zoysia, to be able to compete with the poa anna. If the area stays wet it might also be highly compacted so aerifiying during the summer would be a good idea. If some or all of these problems can't be corrected then you should just live with the poa anna because once you get rid of the poa anna another weed will take it's place if you don't have a healthy turf grass to fill in the area that the poa anna occupied. Eradicating the winter annuals from bermuda (poa anna, chickweed, and henbit) and keeping it out is not a difficult task.You can spray Roundup, buy the concentrate that contains just glyphosate and spray at the low rate, on your dormant bermuda grass at the end of January beginning of February.This is not as scary as it sounds just make sure you don't have any green tissue in the leaves, stems, and stolons. Maybe start small and just spray a couple of spots this year and see how it turns out. As for the henbit and chickweed, Bayer has a broadleaf product with 2,4-D, dimethylamine salt/ Mecoprop-p, dimethylamine salt/ Dicamba, dimethylamine salt. Spray this product mid/late spring when air temps are over 50 degrees. Pendimethalin is the best pre emergent option for the home owner, to keep out poa anna. Pendimethalin is sold as Halts by Scotts. Follow the labeled rate and apply around August 15th water in immediately with half an inch of water. Pendimethalin will also take care of your henbit and chickweed as well.