Landscape Weeds: Control

Cultural weed control methods include mulching, mowing, hand-weeding and cultivation. Mulching suppresses annual weeds by limiting light required for weed establishment. Mowing is an effective method to limit seed production. Mowing must be done when flower heads are produced- April for winter annuals and summer for summer annuals. Frequent hand removal of annual weeds is a time consuming but effective tool if done before flowering. Hand removal of perennials is seldom effective. Often a large part of the root remains in the soil and will quickly regenerate a top.

Before using any chemical product, correctly identify the weed and read the product label. Pre-emergent herbicides are used primarily to control grassy weeds like crabgrass before they germinate. Apply two to four weeks before the plant emerges.

Postemergent herbicides kill weeds present at the time of application. Weeds must be actively growing when the herbicides are applied. Selective, systemic, postemergent herbicides such as 2,4-D, and dicamba offer broadleaf weed control without harming lawngrass. Some, like glyphosate are non-selective and systemic, killing any plant contacted. Others, like diquat, are non-systemic or contact herbicides, killing only plant parts contacted by the herbicide. Contact herbicides are effective against annual weeds but only "burn off" the tops of perennial weeds, chemically mowing them.

Because weeds are opportunists, encourage quick growth of turfgrass or ornamental plants soon after treatment. Otherwise, new weeds will quickly reinfest the area.

Finally, grow a healthy landscape to reduce future weed invasions.

For more information, see the following Colorado State Extension fact sheet(s).

• 3.101 Control weedy grasses in lawns
• 3.106 Weed management for small rural acreages

For more information, see the following Planttalk Colorado™ script(s).  http://www.ext.colostate.edu/ptlk/2117.html