Crabgrass

Q. How can I get rid of crabgrass permanently? I have tried crabgrass poisons and it kills the grass on top but not the root. It's always comes back during the rainy season or if it gets watered on. Thank you for any help you can suggest.

A. Digitaria sanguinalis, our common crabgrass, has seeds which sprout in the spring and summer after rain or watering. It is very fast growing. Likes bare and weak areas of the lawn. It is a noxious weed and crowds out lawn grasses. The stems lie along the ground and root wherever the nodes touch the earth; thus the plants spread rapidly. Even cuttings often take root. The plant dies early in the autumn, leaving brown patches in the lawn

I have recommended this product before, so give it a try:

Bayer Advanced Lawn™ All-In-One Weed Killer for Lawns

Kills Broadleaf Weeds: Dandelion, Chickweeds, and Clovers Grassy Weeds: Crabgrass, Nutgrass/Nutsedge and over 200 other listed broadleaf and grassy weeds

COVERAGE 32 oz. Concentrate treats up to 10,667 sq. ft.

WHERE TO USE: On Lawns (Do not use on St. Augustine (including Floratam), Carpetgrass, Centipede, Creeping Fescue, Dichondra, or desirable clovers)

WHEN TO USE: When weeds are actively growing

Temperature Limitations:
Temperatures above 80 degrees F -- Do not apply on Kentucky Bluegrass, Perennial Ryegrass, or Tall Fescue
Temperatures above 90 degrees F -- Do not apply on Bermuda or Zoysia

http://www.bayeradvanced.com/pg/pg_lp.html#allInOne

I hope this helps with your weed problem.