Dallis grass is a perennial grass with light-green color. Dallis is easily identified by its long seed-heads that protrude from the top. Dallis tends to thrive in wet areas with lots of heat, and grows in circles out from the center of the weed.
Try to improve the drainage of your lawn to take dampness away from the areas were they grow. Additionally, allow the top of the soil to partially dry between each watering to help retain the water only in the root area. Apply pre-emergence fertilizers (usually in the late-spring) to prevent seed germination and growth.
Once weeds are established, pull them by hand and make sure you get the roots as well. After pulling, reseed the area with the comparable grass as to the existing lawns.