Cultural Controls

• The first line of defense against weeds is proper lawn maintenance. Water your lawn deeply but infrequently to prevent shallow grass roots that can be crowded out by weeds. Water early in the morning to prevent water evaporation and allow the vegetation sufficient time to dry before evening. The University of Arkansas Extension suggests plugging bare spots on the lawn with healthy grasses such as Bermuda and St. Augustine. Set your mower height to a high setting to prevent the seeding and growth of weeds. Tall grass limits light to weed seeds, impeding their germination. Lawns cut at a height of 2 inches or less are susceptible to aggressive weeds such as crabgrass.
  
  

Soil Conditions

• Soil compaction encourages knotweed, goosegrass, path rush and bluegrass. Compaction also affects drainage, resulting in the growth of Virginia buttonweed and rushes. Overly saturated soil starves turfgrass of oxygen, allowing weeds to take over. Core aeration reduces soil compaction and improves drainage. A core aerifier is a machine with hollow tines that removes plugs of soil, thereby reducing compaction. The University of Ilinois Extension recommends removal of 15 to 20 cores per square foot.
  
  Low nitrogen levels in the soil encourages the growth of legumes such as white clover. Test the soil to determine nitrogen, phosphorous and potash levels, then choose the appropriate fertilizer for your lawn. Adjust pH levels with lime.
  
  

Herbicides

• Pre-emergent herbicides are applied before weeds have a chance to germinate, whereas post-emergent herbicides are applied directly to weeds. Apply pre-emergents two to four weeks before the germination of weeds. Their effectiveness may be weakened by heat and precipitation, but they offer successful control of barnyard grass, crabgrass and foxtail. Water the pre-emergent herbicide into the grass within two days of application.
  
  Apply post-emergent herbicides to small weeds to control crabgrass and annual grasses. Water the soil the day before applying post-emergent to a depth of 3 inches for best absorption.
  
  

Considerations

• Careful application of herbicides is crucial for your personal safety and the health of your lawn. Certain grasses such as St. Augustine cannot tolerate specific kinds of herbicides. Become familiar with weed identification and read the herbicide's product label to ensure it is appropriate for your turf species. Eradication of weeds entirely is not possible, so a balanced approach is recommended.