University of Maryland Extension

Lawn Herbicides

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Lawn Herbicide Terms
Tips for Lawn Weed Prevention and Management

Herbicides have been used to control lawn weeds since the 1950s. But the potential risks to people, animals, and the environment should cause people to reconsider their use as part of routine lawn care. Concentrating on proper lawn care practices can reduce the need for herbicide use. Herbicides should be used as a last resort and not a substitute for good lawn care. 

If you choose to use an herbicide keep these points in mind

  • The pesticide label is the law. Read and follow the label directions. The information provided is for the safest and most effective use of the product.
  • Select ready-ready-to-use (RTU) products to spot treat weeds eliminating the need for mixing and using a sprayer. If you choose a concentrate product dedicate a sprayer for herbicide use only.
  • Keep herbicides in their original container and purchase the amount needed for only one season.
  • Herbicides work best on young weeds and when the weeds are actively growing. Do not treat drought-stressed lawns.
  • Late summer into fall is a good time to treat difficult weeds like creeping Charlie. Perennial plants move the foods they make, along with what is sprayed onto their leaves, down to their root system as they prepare to go dormant for the winter.   

Herbicide issues

  • During certain weather conditions, volatility or drift can occur causing damage to non-target plants.
  • Some herbicides, such as Dicamba, may damage trees and shrubs when the active ingredient is taken up by roots growing in the treated lawn.
  • Herbicides, especially dry formulations, can wash off treated areas and injure downslope plants.
  • Herbicide can be accidentally tracked into homes by people and pets. Outdoors, synthetic herbicides are broken down by sun, moisture, high temperature, and soil microorganisms. Indoors, the active ingredient can persist, increasing exposure to people and pets.
  • The relative effectiveness of herbicides is subject to many factors outside our control- temperature, rainfall, soil conditions, etc. Even when we fully follow label directions, the resulting level of weed control may be disappointing.

Organic Lawn Herbicides 

 

Organic weed control products are non-selective, contact herbicides. They can also kill turfgrass and are not effective on mature or perennial weeds that have a substantial root system.

The assumption is that organic products are safe to use but that is not always the case. For example, acetic acid based formulations can be caustic and cause skin, eye or lung irritation. Some acetic acid products have the signal word danger (words used to alert consumers of the short-term toxicity of the product)vs. less toxic products that carry a warning or caution on their label.

Active ingredients include

acetic acid (vinegar), botanic oils (clove, cinnamon, rosemary, d-limonene, etc.), HEDTA iron, and potassium salts of fatty acid.

 

Corn gluten has been sold for many years as a preemergent herbicide. It can suppress annual weeds like crabgrass but not as effectively as conventional preemergents. 

Mowing high (maintaining grass at 3-4 inches) during the mowing season, fertilizing, and reseeding bare spots will significantly reduce crabgrass pressure.

Corn gluten is a source of nitrogen. Applying it at the recommended amount to control weeds may exceed the amount of nitrogen allowable in Maryland per the (PDF) Fertilizer Use Act of 2011. For additional information about corn gluten refer to Corn Gluten for Crabgrass Control. 

Synthetic Herbicides

Chemical and trade names to look for on the label. The common name is a simpler version of the chemical name. 

For Grassy Weeds

Preemergents are used for crabgrass and Japanese stiltgrass. Can be used to prevent common chickweed, which is a broadleaf weed. 

Postemergents are used for bermudagrass, nimblewill, and Poa trivialis

Note: sedges such as nutsedge are not grassy weeds  (listed below)

  • Avoid using weed and feed products.
    There are products on the market without nitrogen fertilizer. Look for them in farm supply stores or independent hardware stores.
    • Weed and feeds are not recommended because they are applied in spring (we recommend that most lawn fertilizer be applied in fall) and can contribute to overfertilizing your lawn.
  • Apply prior to seed germination. For crabgrass
    this begins when soil temperatures are above 
    55° to 60°F for 7 to10 days (during and shortly after, forsythia bloom is a rough, but not consistently reliable, guide for application timing).
  • Water after application, according to label.
  • A second application may be possible. Best
    for season-long control. Refer to the product label. 
  • Consult label for specific waiting period between
    application and overseeding.
  • Only siduron (Tupersan) is labeled for application
    on newly seeded turf.

 

Examples

Common Name: Dithiopyr; Trade Name: Dimension (also some control on young crabgrass)

Common Name: Pendimethalin; Trade Name: Halts, others

Common Name: Prodiamine; Trade Name: Barricade

Common Name: Siduron; Trade Name: Tupersan (can be used when sowing grass seed)

Common Name: Benefin; Trade Name: Balan

    Postemergent

    • There are not many options for selective chemical control for perennial grass weeds like bermudagrass (wire grass)roughstalk bluegrass (Poa trivialis), or nimblewill that targets the grassy weed and does not injure the turf.
      • Conventional treatment has been to spray the weedy area using a non-selective herbicide that contains glyphosate killing all of the vegetation. Spray and wait a couple of weeks to see if the vegetation is dead. Spraying at least twice may be necessary. This should be done in late summer into early fall allowing time for the grass seed to germinate and root.

       

    Examples

    Common Name: Quinclorac; Trade Name: Drive

    Common Name: Fenoxaprop-p-ethyl; Trade Name: Acclaim Extra, others

    For Broadleaf Weeds

    Products can contain one ingredient or a combination of active ingredients (combination herbicides are more effective on difficult to control weeds). They can contain a postemergent to control existing weeds and a preemergent to prevent them from developing or can be labeled for both broadleaf and grassy weeds (see ingredients above).

     

    Preemergent

    • To prevent broadleaf weeds in lawns.

    Common Name: Isoxaben; Trade Name: Gallery

    Postemergent 

    • Targets the weeds but does not kill the grass.
    • Apply when daily air temperatures will be between 65° to 85°F. When the temperature is too hot, the herbicide will be more likely to volatilize and damage sensitive plants.
    • Do not apply when precipitation is expected within 24 hours.
    • Do not mow for a few days prior to or after application; and
    • Consult label for specific waiting period between application and overseeding

    Common Name: These active ingredients are found in many herbicides. They can be a single ingredient or be combined to control a broader range of weeds. There are many trade names.

    2,4-D 
    MCPP (mecoprop)
    MCPA
    Dicamba-be careful when using around tree and shrub roots.
    Triclopyr
    Carfentrazone

    Sedges

    Yellow nutsedge and kyllinga are the only significant lawn weeds in this category.

    Postemergent

    • Selective

    Examples

    Common Name: Halosulfuron; Trade Name: Sedgehammer and others

    Common Name: Sulfentrazone

    Non-Selective, vegetation killer

    • kills both grass and weeds

    Common Name: 

    Glyphosate - Used for lawn renovation projects to prepare the area before seeding. However, there are ways to do this without using herbicides. Refer to Lawn (Turfgrass) Removal Methods

    Resources:

    National Pesticide Information Center Active Ingredient Fact Sheets
    National Pesticide Information Center: Weed Control and Herbicides
    Maryland Department of Agriculture pesticide database-Kelly Solutions
    (PDF) HG 101 Guide to Controlling Weeds in Cool Season Turf
    (PDF)TT-49 Broadleaf Weed Control in Established Lawns
    (PDF)TT 46 - Perennial Grass Weeds and Their Control in Turf
    (PDF)TT 43 - Herbicides for Crabgrass and Goosegrass Control in Turf

    References to trade names do not constitute an endorsement or warranty by the University of Maryland.  No discrimination is intended against products not mentioned.

    Home gardeners face many of the same insect pests and plant diseases as commercial growers, arborists, and landscapers. However, some pesticides recommended and labeled for professionals are not labeled or appropriate for gardeners. Pest management practices and recommendations on this website that are “brought to you by…” the Home and Garden Information Center are intended for the general public. Our goal is for all gardeners to learn and practice Integrated Pest Management (IPM) and select the least toxic solutions. If you have questions regarding any pesticide recommendation, contact us at Ask the Experts.

    Tradenames mentioned in this publication are for product identification purposes only. No endorsement is intended.

    Herbicides and active ingredients mentioned are registered in Maryland. Contact your local Extension Service for out-of-state recommendations. 

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