Wednesday, August 6, 2008

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

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