Herbicides

Herbicides are chemicals used to control the growth of weeds and kill them. They work best on actively growing weeds. There are many different kinds of herbicides.

Diagram showing SELECTIVE herbicides that target certain weeds and will not kill plants growing nearby, example: fluazifop targets grasses. Links to 'How they act'.

Diagram showing a NON-SELECTIVE herbicide that knocks down and kills any plants it comes in contact with, example: glyphosate. Links to 'How they act'.

How they act

Contact herbicides
Will only kill the part of the plant they come in contact with.
Example: diquat.

Translocated or systemic herbicides
They move through the plant after being sprayed on the leaves or being taken up by the roots.
Examples: glyphosate, fluazifop.

Pre-emergent herbicides
Designed to kill seeds and underground storage organs, such as rhizomes and bulbs, by direct contact as they germinate or start to grow.
Example: chlorsulfuron.

Post-emergent herbicides
Designed to kill the plant after the seedling stage.
Examples: glyphosate, fluazifop.

How long they last in the soil

Non-residual herbicides
These are quickly inactivated by the soil
Example: glyphosate.

Residual herbicides
These remain active in the soil for varying periods of time depending on the rate of application and the microbial breakdown capacity of the soil.
Example: simazine.

With residual herbicides you will need to wait a period of time before you can replant the soil.