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I think I have Johnsongrass invading my back lawn. I has sprayed the usual Crabgrass/lawn grassy weed killer on it and it is still taking over my entire lawn. What can I do?

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A

Here is a link to Johnson grass control from University of Missouri Extension.  The excerpt below on control emphasizes an integrated approach, that is using many different methods to manage the Johnson grass, there is not a silver bullet but an integrated pest management approach to deal with this weed. 
link to the article is http://extension.missouri.edu/publications/DisplayPub.aspx?P=g4872

Cultural control

Preventing johnsongrass from becoming established in new areas is the best available control method, because the weed spreads in so many ways. Because johnsongrass is a perennial weed, single cultural control measures or herbicide applications rarely provide adequate control.

Johnsongrass control programs should

    * Prevent spread of rhizomes from infested to uninfested areas.
    * Kill or weaken established plants and their underground rhizome system.
    * Control seedlings originating from shattered seed.
    * Prevent production of seed and its spread to new areas.
    * Use fall tillage to bring rhizomes to soil surface, where they may be killed by winter conditions.

These objectives are closely related and are equally important to the success or failure of a control program. In limited infestations, it is possible and desirable to use herbicides to kill the weed and prevent seed production. The critical time to kill johnsongrass is while the weed is becoming established and before it has spread over the entire field. For sites with established infestations, a fall application of Roundup or Touchdown will kill emerged tissue and often developing rhizomes.

Posted on 14 May 2009

Maggie Shao
Horticulture Agent, Salt Lake County

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