Monday, 21 October 2013

Weeds as Indicators of Lawn Problems

Sandra Mason
Extension Educator, Horticulture
Weeds as Indicators of Lawn Problems

One person's weed is another person's wildflower. A weed is just a plant out of place. We have all felt like weeds at times. A rose in a strawberry patch is a weed. The optimist's definition of a weed is a plant whose virtues are yet to be discovered. 

Weeds are just plants having to deal with an unhappy human. Weeds draw scorn, particularly in lawn areas. It is impractical to expect our lawns to be totally weed free all of the time. But according to Tom Voigt, U of I turf specialist, large numbers of weeds in a lawn can indicate certain problems such as:

  • too much traffic
  • improper lawn species selection
  • too much shade
  • unfavorable soil conditions
  • poor lawn management techniques.

Although it doesn't always hold true, certain weeds can be more prevalent under certain conditions. Voigt recommends learning to recognize specific weeds and their favorite conditions to help identify some lawn problems. Correcting these problems can help reduce the need for herbicides. Some of the common conditions and their weed indicators are:

  • Acid soils (bentgrass, red sorrel)
  • Compacted soils (annual bluegrass, bermuda grass, common chickweed, goosegrass, knotweed, mouse-ear chickweed, prostrate spurge)
  • Dry soils (black medic, carpetweed, red sorrel, sandbur)
  • Dry and infertile soils (yarrow)
  • High fertility soil (annual bluegrass, bentgrass, bermudagrass, crabgrass, mallow, purslane)
  • Low fertility soils (plantains, red sorrel, smooth brome, timothy)
  • Low mowing height (annual bluegrass, bentgrass, bermudagrass, crabgrass, white clover)
  • Moist or poorly drained soils (annual bluegrass, bentgrass, common chickweed, crabgrass, goosegrass, ground ivy, mouse-ear chickweed, speedwells, violets, yellow nutsedge)
  • Moist fertile soils (curly dock, henbit, yellow wood sorrel)
  • Moist infertile soil (white clover)
  • Moist shade (annual bluegrass, nimblewill, rough bluegrass, violets)
  • New seedings (barnyard grass, crabgrass, henbit, purslane, yellow foxtail)
  • Shade (annual bluegrass, common chickweed, ground ivy, mouse-ear chickweed, nimblewill, violets)
Some weeds such as dandelions and quackgrass are not particular as to their environment or lawn conditions.

Weed problems can be lessened by proper lawn management. Weeds have a difficult time getting established in healthy competitive lawns. Mechanically removing weeds by hand or hoe can eliminate small numbers of weeds.

Herbicides can be used once proper lawn management and soil condition improvements have been initiated. Broadleaf weeds such as dandelions are often killed by using postemergent herbicides. As with all pesticides–read, understand and follow label directions.

When using postemergent broadleaf products follow these guidelines:
  • Be sure to watch environmental conditions. Watch wind speeds. Often early mornings have less wind. Apply when air temperatures are between 65 and 85 degrees F. Adequate soil moisture is important for the herbicide to work properly. Do not apply when precipitation is expected within 24 hours.
  • Don't mow for a few days prior to application or following application.
  • When possible spot apply with herbicide rather than treating the whole area.
  • Apply these herbicides to new seeded areas only after they have been mowed four times.
  • Wait at least 30 days following application before seeding into areas treated with post emergence broadleaf herbicides. Many broadleaf weeds can also be treated effectively during active growth in autumn.

Realistic expectations about our lawns and proper lawn management techniques can go a long way to control weed problems. Herbicides are another tool in weed control, but not the only tool.

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