Even though the weather is still relatively warm, weeds that trouble lawns during the winter are beginning to germinate. They can overtake and ruin the appearance of the home lawn during the winter. The early fall is the best time to initiate pre-emptive action to control these weeds and to keep your lawn healthy and attractive throughout the winter.
Winter annual weeds, such as annual bluegrass, henbit, common chickweed and others, begin to emerge from seed as the temperatures begin to cool. During the cold of winter, they have a slow rate of growth. As the temperatures begin to rise in February and March, the winter weeds undergo rapid growth.
Winter weeds can cause damage to the turf by competing with it for available sunlight, soil moisture and plant nutrients. Even though the grass appears dormant, grass roots continue to grow and weeds can interfere with their growth. As the weather begins to warm, large mats of weeds begin to die. This can have a detrimental impact to warm season grasses, such as bemudagrass and zoysiagrass, by disrupting the spring green-up process. The turfgrass can be severely stunted or have large dead areas that can easily be infested by summer annuals, such as crabgrass, as well as being more susceptible to insect and diseases.
Keeping the lawn properly maintained will help reduce the weed population. Make sure it receives appropriate amounts of fertilizer and water. Mow at the correct height for the turf species and remove no more than one-third of the leaf blade at each cutting. These practices will increase the effectiveness of using chemical herbicides for weed control.
The use of pre-emergent herbicides, which prevent weeds from germinating, are applied in the early fall prior to the germination of winter weeds to reduce their populations. Generally they are the best method of providing control of grassy weeds in lawns, especially annual bluegrass. Most of these herbicides are in the granular form and usually are watered in after application. Post-emergent herbicides, which control weeds after germinating from seed, are used on an as-needed basis. However, since grassy weeds are very similar to the desirable lawn grasses, control after their emergence is challenging and not always effective. Please follow all label directions and safety precautions when using pesticides.
If you are over-seeding fescue lawns, the pre-emergent herbicides cannot be used since they will also inhibit the germination of the grass 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 fertilizer spreader to distribute the pre-emergent herbicide granules uniformly, and follow the recommended labeled rate. Make sure the application of the pre-emergent herbicide is made before rain is expected or water it in thoroughly with one-half inch of water (if the label directions say so). Poor control of weeds often results from the lack of rain or supplemental watering within seven days of applying the pre-emergent. Do not mow or disturb the soil in any way during or following the first week after the application.
While there is no way to completely prevent every weed from germinating, the application of pre-emergent herbicides combined with the appropriate cultural practices can reduce their infestation during winter.
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.