There are eight main types of herbicide control methods, each have different modes of action.
Here is a short guide to help you select the most effective type as a weed control.
- Translocated or Systemic action is applied as a liquid spray directly to the foliage. The chemical action is translocated through the plants vascular system. This type of weed control is used to clear areas before planting and on troublesome perennial weeds such as Groundelder Aegopodium podagraia. As a non-selective or broad spectrum control it will kill all plants that it is sprayed on, including weeds and precious shrubs etc. An example would be Roundup.
- Selective action is predominately used on lawns to control broadleaf weeds. It only kills dicotyledon plants not monocotyledons (dicotyledon are plants that have two leaves at germination and a webbed vein network, such as Plantain Plantago major. Monocotyledons have one leaf at germination and parallel leaf veins, all grass species and orchids are monocotyledon plants). An example of a selective action weed killer is Weedol/Verdone.
- Contact as the name suggests it is a herbicide that only works on plants that it is directly sprayed on. It does not travel through the plants system. Useful for annual weed cover, but not always strong enough to kill perennial weeds. An example of a contact weed killer is Weedol.
- Residual also called pre and post-emergence weed control. This herbicide leaves a barrier that prevents weed seedlings from germinating. Pre-emergence herbicides are applied in late winter or early spring to kill weed seeds before they germinate. An example of a residual weedkiller is Pathclear. Post-emergence herbicides are used to kill weeds that have already germinated and begun to grow
- Moss control or moss killers have been formulated to control moss in lawns they are sometimes used as a combination of both moss killer and weed control. Applied as a granule. Resolva mosskiller is an example of this.
- Algae control mostly used on hard surfaces to reduce algae growth, generally they have short term results and need to be reapplied regularly.
General note for safe use of pesticides.
- Always read the label
- Always select the correct control method for the types of weeds and different areas that need control.
- Only mix the amount required for the task. Do not store excess.
- Avoid inhalation or contact with skin.
- Spray early in the morning or late at night when bees are in bed.
For further advice and guidance see the Royal Horticultural Society (RHS) for safe use of pesticides at home.
If in doubt, please contact a qualified professional holding a Pesticide Application Qualification (PA1 or PA6).