Do you need it?
Before you go and douse your driveway or garden with a long lasting, residual weed killer you should really ask yourself - do you need it?
Hand weeding is often just as effective - pick the head, pull the root and your done: if you have a lot of weeds or a large area it can be tedious, hard work but it's free!
Let me be square with you - long lasting weed killers work but they are no panacea, they often only keep weeds away for a few months and they also have to be combined with a strong weed killer such as Glyphosate to knock down any existing weeds.
Once you use them, if you don't take the time to fix the underlying problems you are stuck in a never ending cycle of treatment.
Now we've gotten that out of the way, if your still looking for a residual weed killer then read on.
How do long lasting weed killers work?
They leave residues in the soil or on the surface which inhibit new plant growth - that's the jist of it.
I want to be clear - there are NO residual weed killers that work forever, most manufacturers typically state their products will work for 4-6 months.
You can't / shouldn't use these types of weed killer in areas intended to bear vegetation - don't use them on your lawn (it will kill the grass / prevent you fixing dead patches) but they may be useful for killing weeds in artificial lawns.
Typically a long lasting weed killer is applied with Glyphosate, the Glyphosate kills all the actively growing weeds and the residual weed killer protects the area from future plant growth.
What residual weed killers are available in the UK?
Different situations require different products. For example, a long-lasting weed killer may be needed for a soiled area, while a different one may be needed for hard surfaces like block paving or driveways.
These products can contain the same active ingredient, but the delivery method may be different (granules vs. liquid). Here is a list of the best residual weed killers:
Diflufenican is a pre-emergence herbicide used to control broad-leaved weeds in cereals, maize and grassland. It works by preventing weeds from germinating and emerging from the soil.
It has been used since the late 1990s in Europe, Australia, and New Zealand, and is registered for use in many countries around the world. It is typically applied as a pre-emergent herbicide and is known to be highly effective at controlling weeds.
Its use is often combined with other herbicides, such as glyphosate, to achieve greater control of weeds. The herbicide is applied before planting, either as a pre-planting soil treatment or as a seed dressing. It is absorbed by the plants’ roots and prevents their growth.
Diflufenican is most effective when applied before weeds germinate and is most effective in fields with low weed infestation.
Diflufenican is not toxic when used as directed.
Flazasulfuron is a herbicide used for selective control of broadleaf weeds and grasses in cereals, pastures, and other crop areas.
It works by inhibiting the production of essential amino acids, leading to disruption of protein synthesis in susceptible plants. Flazasulfuron has low soil residual activity and is mainly used in post-emergence applications.
It is absorbed by the foliage, roots and shoots of the target plants, and is quickly translocated throughout the plant. It is effective at preventing the growth of broadleaf weeds and grasses, while leaving the crop plants unharmed.
Flazasulfuron is a sulfonylurea herbicide developed by Bayer CropScience and first registered for use in the United States in 1995. It is used for the control of broadleaf weeds and grasses in turf and non-crop areas such as roadsides, pastures, and industrial sites.
Flazasulfuron is a long-lasting, broad-spectrum herbicide that can provide season-long control of weeds. It works best when applied in combination with other herbicides or in multiple applications over time.
Flazasulfuron has been used successfully on many species of broadleaf weeds, including dandelions, chickweed, clover, groundsel, knotweed, lambsquarters, and thistle. It has also been used to control some grassy weeds, such as annual bluegrass, bentgrass, and crabgrass.
It was first developed in the 1950s as a pre-emergence herbicide for controlling weeds in crops. It was later adapted to control weeds in turf and pastures. During the 1970s and 1980s, Propyzamide was used widely in the United States and Europe, and it remained a popular weed killer until restrictions were placed on its use.
In the 1990s, due to concerns about its potential environmental impacts, its use was restricted in the United States, and it is currently only available as a restricted-use pesticide.
In Europe, Propyzamide is still widely used as a pre-emergence herbicide.
It works by preventing weed seeds from germinating, and can remain in the soil for up to two years. It is particularly effective against many common broadleaf weeds, such as dandelions, clover, and thistle.
Propyzamide can be used on turf and ornamental beds, and it is also safe to use around trees and shrubs. When used as directed, propyzamide is an effective and economical way to control weeds over long periods of time.
Salt is often touted as a long lasting weed killer that leaves residues.
The internet is often awash with all sorts of nonsense like homemade weed killers are better than commercial ones - we have tried salt as a weed killer...
Let me just say, it does kind of work: Let me be clear, it isn't anywhere near as effective as a commercial residual weed killer, nor is it as cost effective.
If you use enough salt, it will kill your weeds, it may even prevent new weeds from growing but you need an awful lot of it! The rain will eventually wash it away but salt has been used for centuries as a weed killer - the earliest recorded time is 1850!
How to use them & things to watch out for
So now you know about all the long lasting weed killers in the UK, how do use them?
Firstly - ALWAYS READ THE LABEL, seriously, the first thing you should do is familiarise yourself with the manufacturers guidelines on how much to use, when to use it and where you can use it.
Pay careful attention to other weed killers it can be mixed with, some residual weed killers only work as a pre-emergent herbicide, they won't kill actively growing weeds - you may have to combine it with a strong weed killer like Glyphosate.