Controlling Grassy Weeds in Home Lawns

March 2017


Grassy weeds, such as crabgrass, sandbur, goosegrass, Dallisgrass, annual bluegrass, cheat, and downy brome, interfere with the beauty of turfgrass areas. Herbicides are important tools for controlling weeds in turf, but repeated occurrence of weeds may indicate the turfgrass community has been weakened by some environmental condition, pests, and/or improper maintenance activities. Thus, the first step in control of weeds in turf is a turf management program that produces a dense, vigorous, healthy turf. This can be accomplished by growing an adapted turfgrass variety to your conditions and by properly mowing, watering, and fertilizing. For detailed information concerning the proper care of your lawn, see Fact Sheet HLA-6420 “Lawn Management in Oklahoma.”  The information below was prepared to describe how to control grassy weeds in home lawns with herbicides.

Preemergence Herbicides

Preemergence herbicides were designed to control annual grassy weeds, such as crabgrass, foxtails, goosegrass, and annual bluegrass, while they germinate in the soil. Annual grassy weeds complete their life cycle in one growing season. They come back each year from seed. Commonly used preemergence herbicides include Balan, Betasan, Princep, Surflan, Ronstar, Kerb, Devrinol, and various herbicide and fertilizer combinations formulated for the home owner. It is important to understand which weeds these herbicides can and cannot control. Most preemergence herbicides will consistently control crabgrass, foxtails, and annual bluegrass. These herbicides provided erratic control of sandbur. Only Ronstar will consistently control goosegrass. Nutsedge, a grass-like weed, and Dallisgrass are perennial weeds and are not controlled by preemergence herbicides. These weeds have the capacity to reproduce by underground nutlets and rhizomes, respectively. Generally, perennial weeds are more difficult to control than annual weeds because of their ability to “come back” from underground plant parts.

Correctly applying preemergence herbicides is just as important as knowing which grassy weeds they will control. The proper steps to ensure successful weed control are:

1. Timing of the application is critical because most preemergence herbicides will not control grassy weeds that have germinated and emerged at the time of herbicide application. The ideal time to apply a preemergence herbicide is two weeks before weed seed germination. Crabgrass can germinate from late March to early May, depending on the year and location. A general rule is to apply preemergence herbicides by mid to late March for control of crabgrass and foxtails. Annual bluegrass germinates in late September, if moisture is adequate. Thus, make preemergence herbicide applications by September 15 for the control of annual bluegrass.

2. To ensure the preemergence herbicide of getting into the root-zone soil where weed seed is located, remove excessive layers (thicker than 0.5 inch) of thatch, and also remove debris such as leaves and cuttings before you apply the herbicide.

3. Apply the recommended amount of herbicide on your lawn. Check the product label for this and other information. Applying amounts over the label rate will not result in improved control and may injure or kill bermudagrass. Applying insufficient amounts will result in disappointing weed control. Check the label to be sure the herbicide is safe for use on your lawn. Never apply Kerb, or Princep (simazine) on cool-season turfgrasses, such as tall fescue, Kentucky bluegrass, and perennial ryegrass.

4. Achieve a complete, uniform coverage by dividing the recommended amount of granular herbicide into two equal portions and spreading each in opposite directions. For adequate coverage, make spray applications at approximately 30 gallons per acre or approximately 3 quarts per 1000 ft2.

5. Water in the preemergence herbicide if 1/2 inch of rain does not occur within 24 to 48 hours following application. All preemergence herbicides must be washed into the root-zone soil where weed seed are located.

6. A second application may be required for season long control. This will depend on the particular herbicide and environmental conditions, but generally preemergence herbicides remain effective for 60 to 110 days.

Postemergence Herbicides

Postemergence herbicides are most effective when applied on annual or perennial grassy weeds soon after their emergence, when they are young and actively growing. Since most postemergence herbicides are foliar absorbed, they must remain on the leaf surface for 24 to 48 hours following application for adequate absorption.

Organic Arsenicals

Crabgrass, goosegrass, sandbur, foxtails, nutsedge, Dallisgrass, and other summer grassy weeds are controlled with applications of organic arsenicals (AMA, DSMA, MSMA, etc.) soon after their emergence in May and June. Effective weed control normally involves two to four spray applications, spaced 10 to 14 days apart. The ideal temperature range for effective weed control from these herbicides with minimal risk of injuring your lawn is between 80° and 90°F. The organic arsenicals are safe for use on bermudagrass, buffalograss, and Kentucky bluegrass when applied according to label instructions. Tall fescue and zoysiagrass have marginal tolerance, so injury can occur. Never apply organic arsenicals on centipedegrass or St. Augustinegrass.

Yellow nutsedge can be controlled with applications of organic arsenicals or Basagran in May and June. Johnsongrass can be controlled with Roundup, Kleenup, or other grass killers, but avoid contact on desirable ornamentals and turf.

Kerb

Annual bluegrass, little barley, rescuegrass, cheat, downy brome, and other winter grassy weeds can be controlled in bermudagrass with applications of Kerb in October and

November. Effective weed control may involve more than one application. Since Kerb is root absorbed, “wash” this herbicide into the root-zone soil with 1/2 inch of water within 24 hours following application. Never apply Kerb on tall fescue, Kentucky bluegrass, or perennial ryegrass lawns.

Glyphosate

Annual bluegrass and other winter annual weeds can also be controlled with applications of Glyphosate on fully dormant bermudagrass in December or January. Apply actively growing weeds, which will require several days in which the temperature rises above 50°F. Do not make applications after bermudagrass begins to green-up, and always make applications at the label rate.

 

Grassy WeedHerbicide Control &
Tolerant Turfgrasses
Application Time
Annual bluegrass 1. preemergence herbicides (check label for tolerant turfgrasses)
2. Kerb (use only on bermudagrass)
3. Glyphosate (Roundup)
1. by September 15
2. October - November
3. December - January
Little Barley 1. Kerb (use only on bermudagrass) 2. Glyphosate (Roundup) 1. October - November
2. December - January
Cheat, Downy Brome, and Rescuegrass 1. preemergence herbicides (Princep, safe use on bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass, see label restrictions) atrazine (safe use on dormant common-type bermudagrass, centipedegrass, and St. Augustinegrass.)
2. Kerb (use only on bermudagrass)
1. After October 1
1.1After November 1
2. October - November
Crabgrass and Foxtails 1. preemergence herbicides (check label for tolerant turfgrasses)
2. organic arsenicals (safe use on bermudagrass, buffalograss, and Kentucky bluegrass)
1. by March 15 - April 1
2. May - June
Dallisgrass 1. organic arsenicals (safe use on bermudagrass, buffalograss, and Kentucky bluegrass)1. May - June
Goosegrass1. preemergence herbicides (Ronstar gives most consistent control, safe use on bluegrass, bermudagrass, perennial ryegrass, and St. Augustinegrass)
2. organic arsenicals (safe use on bermudagrass, buffalograss, and Kentucky bluegrass)
1. April 15 - May 1
2. May - June
Sandbur1. preemergence herbicide
2. organic arsenicals (safe use on bermudagrass, buffalograss, and Kentucky bluegrass)
1. by April 1 - April 15
2. May - June
Yellow Nutsedge1. Basagran (safe use on bluegrass, fescue, bermudagrass, centipedegrass, zoysiagrass, ryegrass, and St. Augustinegrass)
2. organic arsenicals (safe use on bermudagrass, buffalograss, and Kentucky bluegrass)
1. May - June
2. May - June

 

OSU Turfgrass Extension Facts

Management 

HLA-6418 Selecting a Lawngrass for Oklahoma

HLA-6419 Establishing a Lawn in Oklahoma

HLA-6420 Lawn Management in Oklahoma

Weed Control

HLA-6421 Controlling Weeds in Home Lawns

HLA-6423 Controlling Grassy Weeds in Home Lawns

Insect Control 

EPP-7306 Ornamental and Lawn Pest Control

 

Robert L. Green

Ornamental-Turf Extension Specialist

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