September and October is a good time to apply controls for the winter annual broadleaf weeds that bloom February through April.
Winter annual broadleaf weeds complete their life cycle within a 12-month period. Seeds germinate in the late summer and early fall; plants grow during the winter and flower the following spring. Control measures implemented in the fall are often more effective than those applied in the spring once flowering has initiated. Young, actively growing plants are more readily controlled than fully mature, flowering plants.
Many winter annual broadleaf weeds are prolific seed producers. If not controlled, plants will produce seed in the spring that will remain in the soil until environmental conditions are appropriate for germination. Controlling winter annual broadleaf weeds before seed set will reduce future weed problems.
The most common annual broadleaf turfgrass weeds are common chickweed, corn speedweed, henbit, purple deadnettle and shepherd’s purse. Proper weed identification is an essential step in weed control. An excellent resource for identification for turfgrass weeds found in Tennessee, is tennesseeturfgrassweeds.org.
The first line of control is through good lawn care throughout the year. The most common recommendations are implementing proper fertilization, follow good mowing practices and irrigate as necessary during the summer months. These practices will lead to the development of a healthy, dense turfgrass. Turfgrass density will reduce the number of voids in the lawn canopy for winter annual broadleaf weeds to invade. Overseeding warm-season turfgrass species like bermudagrass with cool-season species like perennial ryegrass can help reduce winter annual broadleaf weed problems.
Pre-emergent herbicides can also be used to control the winter annual broadleaf weeds. Pre-emergent herbicides must be applied before germination of the cool season weed seed. These products should be applied in late summer. A note of caution, if planning to renovate a cool season lawn during the fall, do not use a pre-emergent herbicide. Also, do not use these products on warmseason lawn grasses that are to be overseeded.
Numerous herbicides are available for postemergent control of winter annual broadleaf weeds.
When applied early in the life cycle of young plants, these herbicides can be highly effective. Always check the product label for specific turfgrass tolerance information.
These materials can injure surrounding desirable vegetation. Read label carefully and do not apply herbicides underneath or around desired vegetation or in conditions that favor herbicide drift or volatility – high winds or temperatures greater than 85 degrees. While granular fertilizers containing herbicides are available, efficacy is significantly greater when these herbicides are applied as liquids.
In summary, the use of proper maintenance practices throughout the summer will help prevent the encroachment of winter annual broadleaf weeds in the fall. When control measures are needed they should be used before these weeds produce seeds that can be deposited into the soil seed-bank. Read and follow label directions on any control product that may be used.
For more information, contact the UT-TSU Extension Office in Wilson County at 615-444-9584. You can also find us on Facebook or visit extension.tennessee.edu/wilson.
Ruth Correll, UT Extension-TSU Cooperative Extension agent in Wilson County, may be reached at 615-444-9584 or firstname.lastname@example.org.