Turf and Landscape - Plan Now for Winter Annual Weed Control

Winter Annual Weeds will be starting to germinate in late August and will continue through the fall. Now is the time to plan control programs. The following is information on the subject.

Winter annual broadleaf weeds of turf and landscapes include common chickweed, henbit, purple deadnettle, field violet, annual speedwells (corn, ivyleaf, purslane, and Persian speedwells), and mustard family weeds including wild mustard, wild radish, bittercress, yellow rocket, and shepard’s purse. Winter annual grasses include annual bluegrass, annual ryegrass, and downy brome. Several short lived perennials and biennials will also be germinating during this time such as mouseear chickweed and marestail (horseweed).

Preemergence herbicides can be effective in reducing late germinating winter annuals; however, many of these weeds germinate from fall through spring requiring longer residuals. Dithiopyr, pendimethalin, or prodiamine are recommended as late summer applications for the control of annual bluegrass in established turf . OH2 and Rout are examples of preemergence materials highly effect in landscapes on mustard family weeds, speedwells, Lamiums (henbit and purple deadnettle), horseweed, and annual bluegrass. They are weak however on chickweed which is better controlled with herbicides containing isoxaben (Snapshot, Gallery), pendamethalin (Pendulum, others), trifluralin (Snapshot, others), or prodiamine (Barricade). Check with each product label for compatibility with specific landscape plants and efficacy on specific winter annual weeds. Often it is more economical to allow cool season weeds to germinate and then use a post emergence herbicide. In turf, broadleaf herbicide combination products are effective on winter broadleaf weeds when applied in the fall or early spring. Non-selective herbicides (such as glyphosate) can be used for winter weed control in landscape beds with minimal cautions after leaf drop in deciduous plantings and as directed applications around evergreens.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County

Turf and Landscape - Bittercress

The following is information on controlling bittercress in turf and landscape beds.

One winter annual weed that has become increasing problematic over the past through years in turfgrass and landscape beds is hairy bittercress. This weed grows in a rosette and is generally not noticed in turfgrass sites until it produces a flower stalk in March/April. Fall or Spring applications of 2.4-D will control emerged bittercress but will not prevent subsequent germination from the soil seed bank. Although an expensive proposition, September applications of Gallery will provide residual control of this weed as well as other winter annuals but not wild Garlic. In landscape beds an early spring application (prior to bittercress flowering) of organic mulch applied at 3 to 4 inches will smother and provide suppression of this weed. More effective control can be obtained with September applications of herbicides such as Snapshot, OH2, or Rout. Always consult the herbicide label to see if all desired plants within the bed are tolerant
to these herbicides. All winter annuals can be effectively controlled with non-selective herbicides such as Roundup, but make sure the spray does not contact desired plants.

Extracted from an article by Stephen E. Hart, Ph.D., Specialist in Weed Science and Patrick McCullough, Program Associate in Weed Science, Rutgers University in the March 13, 2008 edition of the Plant and Pest Advisory, Landscape, Nursery and Turf Edition.
http://njaes.rutgers.edu/pubs/plantandpestadvisory/2008/ln0313.pdf

Landscape, Turf, and Nursery - Winter Annual Weeds: Bittercress

Bittercress is a common winter annual weed that can proliferate in landscapes, turf areas, and nurseries. Below is a picture of this common weed that is now in flower in Delaware.

Picture from the Woody Ornamental Pest Scouting Report from Penn State University