Answer: Your best defense is a thick healthy lawn so to prevent weeds in the future, put your lawn on a regular maintenance schedule of watering, feeding and mowing. WSU recommends feeding in April, June, September and December with a 3-1-2 ratio of NPK. Water deeply once or twice each week and mow regularly to encourage healthy growth. To address your current weed problems, ou must be aggressive in dealing with quackgrass, since it is aggressive. Unfortunately, there are no selective herbicides for quackgrass and with its rhizomatous root system, it is almost impossible to pull. The only real alternative in dealing with quackgrass is killing it with a nonselective herbicide such as Roundup or Finale. Keep in mind that these herbicides will kill anything with leaves, including any grass it touches.
Quackgrass, like crabgrass, leaves thousands of seeds in the lawn for the new season. Pre-emergence herbicides, such as crabgrass preventers, will inhibit germination of quackgrass seed. Such seeds germinate as the soil temperature reaches around 55-60 degrees in spring, so timely application is important.
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