Quackgrass is one of those weeds that reminds you of the bubonic plague. It is hideously difficult to prevent from spreading. You literally almost have to manually pull up every plant and then treat the lawn with an herbicide to kill anything that you might have left in the lawn. The best key for quackgrass control in lawns is to work on preventing the spreading of the weed in the first place. If you can keep it out before it gets it, you will have a much easier time controlling it. The best way to do this is to practice the best maintenance techniques for your lawn so that it is healthy and void of conditions that encourage weeds to grow in it. Some of those things include fertilizing your lawn regularly, watering deep and infrequently, mowing high and often, and choosing the right type of grass for your climate and yard conditions.