Often during the winter months, numerous annual weeds infest lawns and gardens just as bad as warmer weather weeds. Fall is the time to take preemptive action to control these unsightly weeds from emerging.
Winter annual weeds, such as annual bluegrass, henbit, lawn burweed (spurweed), common chickweed and others, begin to emerge from seed when our warm season lawns enter dormancy during the fall months. The winter weeds begin to germinate in early fall because the temperatures begin to cool. During the cold months of the winter, growth is slow; but as temperatures slowly begin to warm up in February and March, the winter annuals begin to initiate rapid growth and development.
Winter weeds can be very damaging to the turf grasses in addition to destroying the beauty of the lawn. They compete intensely with the turf grass for sunlight, soil moisture and plant nutrients during this time period. Even though the turf appears dormant, the roots continue to grow and function and the weeds interfere with the growth and development of the roots.
As the weather begins to warm, large mats of these weeds die out. The warm-season turfgrass can be severely stunted or have large openings 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. Use post-emergent herbicides (chemicals that are applied to the weeds after germination from seed) to control on an as needed basis.
On fescue lawns, if you are overseeding, the pre-emergent herbicides cannot be used since they will inhibit the germination of fescue seed. 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 granules uniformly, and follow the recommended rate.
Make sure the application of the pre-emergent herbicide is before rain is expected, or water it in with 1⁄2-inch of irrigation water. Also, do not mow or disturb the soil following the application. Doing so will reduce its effectiveness.
Remember, always read herbicide labels carefully before use, and follow all safety precautions.
Timothy Daly 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.