Types of Herbicides

Herbicides are used to kill unwanted vegetation. Herbicides are distributed through sprays or granules. Different types of herbicides have been developed to meet specific needs for maintaining a weed-free lawn and garden. When applying herbicides, take precautions against exposure. Do not use herbicides on windy days, just after rainfall or after watering.

Pre-emergent Herbicides

The effectiveness of a pre-emergent herbicide lies in applying the chemical mix at the appropriate time. A pre-emergent works on germinating weed seeds and is commonly found in granular form. It is ineffective against dormant seeds. Apply a pre-emergent herbicide when your lawn is in the early stages of new growth, just after the dormancy stage. In colder climates, apply a pre-emergent after any danger of frost and your lawn begins to exhibit new growth. In warmer climates, apply the herbicide in the early spring just as your summer lawn is emerging.

Post-emergent Herbicides

Apply this type of herbicide directly to the weed or undesired plant. These herbicides are available in spray form, and work in one of two ways. They may be systemic, in which the chemicals disrupt growth processes within the plant, such as photosynthesis or cellular production. They may also work on contact, in which just the vegetative components that come in contact with the spray are affected. For a contact spray to be effective, the entire plant must be sprayed.

Selective Herbicides

Selective herbicides are designed to eliminate broadleaf weeds such as prickly lettuce and sowthistle. Application of a selective herbicide allows you to target these weeds without killing the surrounding vegetation, usually your lawn turf. Selective herbicides may cause the weed to "overgrow" by accelerating its growth processes, resulting in the weed dying from over-production of bio-chemicals. Selective herbicides may also disrupt the photosynthesis process, effectively causing a toxic build-up of specific bio-chemicals within the targeted group of plants.

Non-selective Herbicides

These are broad-spectrum herbicides and will kill any vegetation in which they come into contact. Such herbicides may be used to clear an area of grasses, weeds, flowering plants and any other form of vegetation. Post-emergent herbicides may be non-selective herbicides. Do not use these types of sprays indiscriminately. The chemical spray may be carried on the wind or spread through water in wet ground. Another type of non-selective herbicide is the total vegetation herbicide. These chemical compounds are designed to kill any vegetation in which it comes into contact and sterilize the soil for a period of time.

Keywords: types of herbicides, pre-emergent herbicides, selective herbicides

About this Author

Shelly McRae resides in Phoenix, Ariz. Having earned her associate's degree from Glendale Community College with a major in graphic design and technical writing, she turned to online writing. Her credits include articles for 123Life.com, eHow.com and several non-commercial sites. Her work background also includes experience in the home improvement industry and hydroponic gardening.