It's too hot to use broad-leaf herbicides. You can't use pre-emergents with flood irrigation because it washes the pre-emergent out of the sprouting zone.

Hand weeding and mowing at the right height for new Bermuda will keep the weeds under control. As the Bermuda spreads, it can crowd out most weeds.

Next year you probably won't have much of a problem.

We bought our irrigated property in the fall of 09. Had to establish pasture and lawn pretty much from scratch. Yes at first you will get lots of weeds, not a whole lot you can do in the beginning but be patient. Fertilize and let the bermuda crowd it out. Most of our property is pretty weed free almost 2 years after putting in the lawn but there is still room improvement. I've been practicing my hoeing skills lately. Bout all you can do. Plant lots of fruit trees and relish how easy it is to grow them. It makes the less than perfect lawn more bareable. ;-)