Systemic (translocated) Weedkillers
The active ingredient is taken up by the foliage and transported down to the rest of the plant including the perenniating stems and roots which allow some plants to survive adverse conditions. There should be plenty of foliage so that the maximum amount of active ingredient is absorbed and it must be allowed to continue to grow until it is well on the way to extinction (so this is also known as a post-emergent herbicide). It could be two to three weeks before the weeds are completely dead, but they can be removed after about six days when signs of yellowing and wilting may begin, and any remaining parts should not recover. In the meantime they may produce seeds, especially fast maturing ephemeral weeds like Hairy Bittercress, or any weeds which are in flower so removing them before application would be advised - a mower at its highest setting or a line trimmer held high could be used for a large area. Also if the area has been infested for some time there will be a reservoir of seed which will germinate later - turning over the soil and applying a mulch should greatly reduce this occurrence. If you are an impatient gardener or follow the school of the instant 'makeover', then this type of herbicide may not suit unless you plan ahead and treat the weeds a few weeks beforehand.
(LD50 stands for Lethal Dose 50 which is the amount that kills 50% of test mice given the substance being assessed.)
Sometimes called pre-emergence herbicides, they are non-selective and remain in the soil, killing germinating seeds and shoots from perennial roots. Some can be used with care around established shrubs and trees, but not where bulbs are planted. Usually they are used in combination with other weedkillers on paths and gravel and should keep them relatively weed-free for the growing season if applied in the spring. They can be transported through the soil by percolating water and in surface run-off, so care must be taken near bodies of water and streams. The rate of movement will depend on a number of factors such as soil type and the organic content. Also grass and flowerbeds next to treated areas can be affected (The roots of shrubs which are growing under treated gravel paths, can show signs of damage such as white blotches on the leaves).
|Trade Name**||Type||Active Ingredient(s)||Use|
|B&Q Complete||Systemic||Glyphosate||general and spot weeder|
|Gramoxone||Contact||Paraquat||fast acting ground clearance (agricultural use only), perennial weeds not completely killed|
|Pathclear||Systemic and Residual||Glyphosate, Diflufenican and Oxadiazon||paths and gravel|
|Roundup||Systemic||Glyphosate||general to clear for planting and as a spot weeder|
|Tumbleweed||Systemic||Glyphosate||general to clear for planting and as a spot weeder|
|Weedol||Contact||Diquat||fast acting ground clearance, perennial weeds not completely killed|
|Weedol MAX||Contact||Pelargonic acid||fast acting, perennial weeds not completely killed|
** These are some of the products available and not a recommendation for their use.