Types of Herbicide

Herbicides offer the homeowner another option to fight nuisance plants. These chemical compounds attack weeds in the lawn or garden to kill the plant and prevent future infestations. Manufacturers make different types of herbicides for different applications in the landscape. These chemicals include toxic materials that must be handled properly and applied to the landscape following manufacturer recommendations.

Pre-Emergent Herbicide

Weeds lie dormant under the soil surface during the cooler months of the year. The warming sun of springtime causes weed seeds to germinate much like annual and perennial plant seeds. Like all plants, weeds are at their most vulnerable when in the germination or seedling stage. Pre-emergent herbicides attack weeds at the point of germination. This type of herbicide works best on annual weeds.

Post-Emergent Herbicide

Most gardeners discover weeds infesting a garden when these unwanted plants pop their heads well above the soil. Post-emergent herbicides tackle the task of removing weeds at the juvenile and mature stage. Juvenile weeds include plants that haven't produced seeds yet but have leaves visible above the soil level. Mature weeds produce seeds that quickly compound the weed problem with further seed setting and germination. Post-emergent herbicides contain chemicals that attack foliage first by absorption through the leaves during active growth phases of the plant. Post-emergent herbicides typically come in spray formulas and fall into the category of contact herbicides to kill foliage above ground. Systemic post-emergent herbicides soak into the leaves and travel to the roots of the plant. Care must be used to protect ornamental plants since many types of post-emergent herbicides kill every plant with spray contact on the foliage.

Non-Selective Herbicide

Non-selective herbicides include products that don't discriminate between weeds and regular plants. These herbicides include both pre- and post-emergent types that kill annual and perennial weeds. Liberal use of non-selective herbicides in a flower garden will almost always result in damage to existing plants. Many gardeners place a bucket over treasured plants as protection from over-spray.

Selective Herbicide

Selective herbicides include a class of weed killers that attack specific nuisance plants. Homeowners frequently use selective herbicides to kill weed plants such as clover, dandelion and creeping Charlie in the lawn. Selective herbicides won't harm the grass with application. Extreme care must be used to limit exposure to trees, shrubs and flowers when using selective herbicides. Instruction labels include exactly which weeds each type of selective herbicide will kill as well as warnings about exposure to ornamental plants.

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About this Author

S.F. Heron is an avid gardener with three years of experience in online writing and a working background in aviation and earth and ocean sciences. She is published on various sites, including Helium, eHow and Xomba. She holds a Bachelor of Science degree in journalism from the University of Maryland.