herbicide jugs
Updated: May 11, 2022

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. 

Critical herbicide information and cautions

  • The first step is to identify the weed. That will help to determine the best herbicide for the job. See Weed Identification Photos
  • 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. Learn more about herbicides for weed control from the National Pesticide Information Center. 
  • 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.
  • Weed and feed products are not recommended because they:
    • are formulated to treat the entire yard
    • are applied in spring (we recommend that most lawn fertilizers be applied in fall)
    • can contribute to overfertilizing your lawn
  • Always read and follow the label directions of any herbicide product you are using!
  • 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.   

The problems with herbicide use

  • 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. Synthetic herbicides are broken down by the 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.
  • Weeds develop resistance to herbicides making them less effective.

Lawn herbicide terms found on a product label

Terms Terms for reading the product label
Active ingredient

Is the chemical contained in the product that controls the target weeds. There can be more than one active ingredient. There are many combination products on the market.

Chemical name(only one chemical name)

A complex technical description of the active ingredient contained in an herbicide.

chemical herbicide active ingredients
Common name(only one common name) A simpler version of the chemical name. See chemical name above.
Trade name A name used by the manufacturer of an herbicide for marketing purposes.  Active ingredients can be sold under many trade names.

Mode of Action

 

 Selective or Non-Selective - for lawn weeds a selective herbicide is preferred.

Contact herbicide Affects only the portion of the green plant tissue to which the herbicide was applied. They can ‘burn down’ the tops, but they cannot move within the plant’s vascular system and cannot kill the root, rhizomes or tubers of perennial plants. Vinegar and potassium salts of fatty acids are examples of organic contact herbicides. Effective against young, annual weeds, a poor choice for perennial weeds. 
Systemic herbicide

Are translocated or moved within the plant’s vascular system.  

When applied in the late summer and fall to foliage the herbicide will translocate to the root system providing better control of perennial, difficult to control weeds. Can be selective or non-selective. May take weeks to kill the target weed.

systemic herbicide label
Nonselective herbicide

Kills or injures all plants, whether they are broadleaved or grassy, target and non-target that come in contact with the herbicide. Glyphosate, diquat, and vinegar are some examples. Glyphosate is typically used in preparation for total lawn renovation. These are usually not used on grass as they also will kill desirable turf grass.

Glyphosate (Roundup®) Information and Alternatives for Weed Management

Selective herbicide

Kills or damages certain plant species without seriously harming others. Often used to selectively kill broadleaf weeds growing in turf without injuring the grass. 2,4-D, Triclopyr, and Dicamba are some examples.

Timing of Application

 

Preemergent herbicide

Applied before the weeds begin to germinate. 
Timing of application is important for effective control. Commonly used in the spring to control crabgrass and some broadleaf weeds.

preemergent herbicide label
Postemergent
herbicide
Applied directly to the foliage of weeds that have germinated. They can be selective or non-selective and work more effectively when the weeds are actively growing and not drought stressed.

Trends in homeowner herbicides

Manufacturers of lawn herbicides labeled for homeowner use are formulating more combination products. They contain a number of the active ingredients listed below under 'chemical options' and can control or suppress a large number of different weeds. There are combo products labeled to control both grassy and broadleaf weeds.  Some even contain both a postemergent and a preemergent for controlling existing weeds and preventing those that return from seed. Read and follow the label directions of the product you select. Look on the label for important information regarding the following: cautions, timing of application, weeds controlled or prevented, where to use, dilution rate (if a concentrate), watering, mowing and reseeding instructions.

Organic and chemical herbicides

Organic lawn herbicides 

 

Organic weed control products are non-selective, contact herbicides. They can also impact or temporarily discolor turfgrass. Organic herbicides are best applied to young weeds and most likely, repeated applications will be needed according to the label directions. 

 

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 is not as effective 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 Maryland's Lawn Fertilizer Law. For additional information about corn gluten refer to Corn Gluten for Crabgrass Control.

Synthetic (chemical) 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)

Preemergents
  • 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 fertilizers 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 to 10 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 a specific waiting period between
    application and overseeding.

 

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: Benefin; Trade Name: Balan

 

Postemergent
  • There are not many options for selective chemical control for perennial grass weeds like bermudagrass (wiregrass), 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 weeds that are difficult to control). 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