During the winter months, numerous weeds infest lawns and can be just as bad as the warm weather lawn weeds. The early fall is the time to take pre-emptive action to control these weeds.
Winter annual weeds, such as annual bluegrass, henbit, common chickweed and others, begin to emerge from seed in early fall as the temperatures begin to cool. During the cold months of winter, growth is slow; but as temperatures slowly begin to warm up in February and March, the winter weeds begin to rapidly grow and develop.
Winter weeds can damage the turf grass in addition to destroying the beauty of the lawn because they compete with the turf grass for available sunlight, soil moisture and plant nutrients. Even though the turf appears dormant, the roots continue to grow and function and the weeds interfere with development. As the weather begins to warm, large mats of these weeds begin to die out. The warm-season turfgrass can be severely stunted or have large dead areas that can easily be infested by summer annuals such as crabgrass, in addition to being more susceptible to insects, diseases, and environmental stresses.
Numerous herbicides may be used to control winter annual weeds. Options include the use of pre-emergent herbicides (chemicals that prevent weeds from growing), such as Surflan, Balan, and Halts applied in the early fall prior to winter annual weed germination. The use of post-emergent herbicides (chemicals that are applied to the weeds after germination from seed)is used for control on an as needed basis for weeds, except for annual bluegrass which is best controlled by pre-emergent applications of herbicides.
If you are over-seeding fescue lawns, the pre-emergent herbicides can not be used since they will inhibit the germination of the seeds. Control options are limited, so the best way to deal with weeds is to apply post emergent weed killers to control broadleaf weeds.
Use a mechanical fertilizer spreader to distribute the pre-emergent herbicide granules uniformly, and follow the recommended rate. Make sure the application of the pre-emergent herbicide is made before rain is expected or water it in thoroughly with 1/2 inch of water. Poor control of weeds often results from the lack of rain or supplemental watering within 7 days of the pre-emergent application. Also, do not mow or disturb the soil during or following the application within the first week. Doing so will reduce its effectiveness.
The control of winter weeds is best accomplished by applying pre-emergent herbicides now to prevent them from becoming established in the lawn. Remember, always read pesticide labels carefully before use. Follow all safety precautions.
Timothy Daly, MS is an agricultural and natural resource agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010 or firstname.lastname@example.org.