Pre-Emergent Grass Herbicide Products

Pre-emergent Herbicides

• The Ohio State University Extension recommends a number of pre-emergent herbicides for weed control in grass. These include bensulide, DCPA, benefin, pendimethalin, siduron and oxadiazon. All chemicals are sold under different tradenames and are safe for use on a variety of grass types such as perennial ryegrass, Kentucky bluegrass, tall fescue and most fine fescue varieties. Siduron is the only herbicide that may also be used at the time of lawn seeding, as it does not harm desirable grass seeds or seedlings.

Timing for Annual Weeds

• Timing the application of pre-emergent herbicides is crucial for effective control. This timing differs with the type of weed. Annual weeds may be summer annuals or winter annuals. Germination of summer annuals such as crabgrass and knotweed occurs in spring, while the winter annuals germinate in fall. Apply pre-emergent herbicides for summer annuals during early spring, as early as March 1. Apply the herbicide for winter annuals such as common chickweed and annual bluegrass during late summer or early fall.

Timing for Biennial Weeds

• Biennial weeds have a lifespan of two years. The plants germinate and grow foliage during the first year and then produce flowers and seeds during the second year before dying. Dandelion is a common biennial weed, but the plant can persist for several years. Apply pre-emergent herbicides for biennial weeds throughout the growing season because the seeds are produced and germinate all through the season.

Timing for Perennial Weeds

• The control of perennial weeds is difficult with pre-emergent herbicides because these plants spread with seeds as well as vegetatively with spreading roots. These vegetative propagation nodes remain unaffected by herbicides. To control the germination of seed, apply pre-emergent herbicides during spring. Perennial weeds include field bindweed, or the morning glory weed, and Canada thistle.