Managing weeds can be an easy task or just about impossible.  It all depends your  lawn maintenance, watering, and fertilizing.  First of all and most important is proper watering.   Too much watering and your weeds are going to spread at a very fast rate to little and your grass will thin out allowing weeds to fill in the empty areas.  In the summer when the rains are hear I like to set my rain censor at the about  1/8 of an inch that is the lowest it will go, so when it does rain the censor will immediately shut the system off not wasting water and not watering too much.  When it does rain everyday you will get a little bit of weeds it all depends on the thickness of your grass.  The thicker the grass the less weeds you will have .  The weeds that you do get in the summer, it is always better to spot treat the weeds than blanket spray.  Blanket spraying  in the high heat could damage your turf if you go at a high rate with your herbicide.   The best herbicides that I have use in the summer is Celsius and mansion.  They are both good and get rid of weeds pretty fast.  If you go into a drought and your grass looks stressed out never use herbicides, just wait until it cools down or you get some rain and turf heals up.  During the dry warm season Apr-June and Sep-Nov is the time when I put the rain censor to 1 inch and maximize my watering. This will keep your grass from getting stressed out.  I normally say  about 2 days week of watering is fine, but on these months i always put them on three days.  When the cold fronts start coming and the temp is nice and cool than 2 days a week of watering is fine.  During the cool months you can put a lot better herbicides on your turf.  Atrazine is the best herbicide for the winter and also has a pre emergent in it which will prevent weeds for germinating.  Applying a  high Nitrogen fertilizer in the cool months is also a good way to control weeds because the nitrogen will burn out some of the weeds.  Applying a high nitrogen fertilizer in the high heat is not a great idea because it will acutually make your weeds spread and may burn your grass.  Proper mowing height is also important.  In the summer I always start raising the height of my grass and as it cools down I will lower the height.  I you cut higher it will strengthen your roots of your grass allowing it to be thicker and less weeds.  The proper mowing for floratam is 3.5 inches in the winter and 4.0 to 4.25 in the summer.  Zoysia grass is about 1.5 inch in the winter and 2.5 to 3.0 inch in the summer.  The zoysia grass is doing very well when properly maintained.  I almost never get weeds from that grass because it grows so thick.