Weeds are opportunist plants that take advantage of thin, bare patches of lawn grass. Weeds can invade a home lawn environment for many reasons, including improper mowing, watering and fertilizing; insect and disease damage; compacted soil; excessive wear; environmental stress and excessive thatch. Types of weed control include environmental, mechanical and chemical methods.
Environmental control is the first line of preventive defense against lawn weeds and involves creating optimal conditions for the growth of grass. The most important environmental control is the selection of the right grass seed that will be a successful competitor with local weeds. Additional environmental controls that will aid in the growth of grass include mowing the lawn to a higher level, maintaining a topsoil pH of between 6 and 7, and properly watering, aerating and fertilizing of the lawn area.
Mechanical control refers to frequent lawn maintenance methods that provide both for the prevention and removal of weeds. Mowing the lawn to the correct height, 2 to 3 inches for most lawns, is a mechanical and environment control that has a big impact of the health of the lawn grass. The height of the top growth is directly related to the depth of the grass roots. The deeper the grass roots, the more established the turfgrass and the more difficult it is for weeds to invade. Another mechanical control involves the hand pulling of lawn weeds as they appear to prevent any spreading.
Chemical Control - Pre-emergent
Pre-emergent chemical control is the use of herbicides to prevent the future germination of lawn weeds. Pre-emergent herbicides are primarily used to prevent annual grassy weeds and annual broad-leaf weeds. Apply the herbicide 2 to 3 weeks prior to the expected weed germination. Heavily water the lawn several days after the treatment. Pre-emergent herbicides have no effect on weeds after germination.
Chemical Control - Post-emergent
Post-emergent chemical control is the use of herbicides to kill lawn weeds that have already germinated and emerged from the top soil. Post-emergent herbicides kill perennial grass weeds, broad-leaf weeds and annual grassy weeds. Post-emergent herbicides are most effective when the weeds are young and growing, the topsoil is moist and the ambient air temperature is warm. Apply the herbicide directly on the weed foliage and wait 2 to 3 days to mow the lawn after treatment. Post-emergent herbicides have no effect on weeds that have yet to germinate.