Published: 9 Feb 2018
Herbicides can be broadly divided into selective and non-selective herbicides, meaning that some only kill certain types of plants such as grasses, whereas others are broad spectrum and kill all plants they contact. They can also be grouped by their mode of action (MOA).
Contact herbicides kill plant tissue on contact and are often quick acting. They have limited movement in the plant and usually have no soil activity. Selectivity is limited but they can be used to control small annual weeds in well-established annual or perennial pastures or crops.
Translocated herbicides are taken up by one part of the plant and moved to other parts; some are more active via the foliage whereas others are more active via the roots.
Soil-active herbicides act on seeds or roots and/or shoots of germinating weeds, or roots of established weeds.
Soil-residual herbicides are soil-active herbicides which remain active over a period of time. The length of the residual action depends mainly on the nature of the chemical itself, the rates applied, the climate, the properties of the soil, e.g. high or low in clay or organic matter, and the rate of uptake by the weeds. Residual activity is particularly important when considering subsequent crops and pastures.
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