University of Maryland Extension

Lawn Herbicide Terms

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 names

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 herbicideAffects 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.  systemic herbicide

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. 

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.

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. 
preemergent herbicideTiming of application is important for effective control. Commonly used in the spring to control crabgrass and some broadleaf weeds.

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.

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