In Brighton, down the road from our HQ, the battle over weeds continues with Labour councillor Tim Rowkins last week estimating that the council now faces £60 million worth of repairs to pavements damaged by weeds:
Untreated weeds fuel £60 million pavement repairs backlog – Brighton and Hove News
The council stopped using the herbicide glyphosate (also known as Roundup) back in 2019 and, since that time, the weeds have run wild, causing extensive damage to pavements which are proving a hazard to local residents, a number of whom have tripped and fallen while others have found it impossible to manoeuvre mobility vehicles, wheelchairs and buggies along them.
Having tried big weed ripping machines and manual weeding (staff are reported to be suffering from repetitive strain injury with the latter and can only do the work for two hours) Brighton has decided that it has no choice but to bring back herbicide usage, this time using controlled droplet application (CDA) spraying methods which it claims can greatly reduce the amount of glyphosate used.
So what is the difference between CDA/ULV sprayers and ‘normal’ methods of application and is it possible to use less herbicide such as glyphosate?
CDA/ULV sprayers will typically spray the neat undiluted herbicide. When applying something like glyphosate 480 you would heavily dilute the chemical with water at least 20:1 and above. The level of dilution will depend on your overall spray rate from your sprayer. In some situations, you will be spraying up to 250 litres of liquid per hectare to deliver 3 or 4 litres of active ingredients.
CDA / ULV sprayers have a much lower flow rate that allow the neat chemical to be sprayed without bulking it up with water. So, you can deliver just the active ingredient sprayed neat. This is impossible with conventional sprayers because they cannot get down to the incredibly low flow rates required. It is also impossible with simple CDA sprayers for the same reason. With basic CDA sprayers the active ingredient still needs to be dilute, not as much as with standard sprayers for sure, but still it cannot be sprayed neat because a standard CDA sprayer will not be able to get down to the very low spray volumes required for neat spraying. Only a CDA/ULV sprayer will do this.
But regardless this would not, on the face of it, reduce the amount of actual chemical you need per unit area. Sure, you remove the hassle of mixing it with water and the energy needed to spray the much larger volume of mixed solution but that won’t affect the actual amount of active ingredient being sprayed. Right?
It’s all about the spray properties
Well, no. CDA spraying in general allows you to use much less of the overall active ingredient per unit area and get the same results. And with a CDA/ULV sprayer this reduction of active ingredient usage per hectare is enhanced even further. To explain how this is possible we need to look at the characteristics of the sprays produced.
The first important characteristic is that the ULV/CDA overall volume of spray per unit area is much lower, sometimes as much as 250 times less actual fluid is sprayed. This means that there is far less opportunity for any liquid to flow off the leaves it hits. Very small volumes of liquid will not have a chance to agglomerate and flow away, they will stick to the leaves much better. This dramatically reduces run off.
The next characteristic is droplet size or, more precisely, the range of drop sizes produced. CDA sprayers will be configured to deliver drop sizes of between 140 and 160 microns. This is an ideal balance between having droplets small enough to penetrate foliage and stick to the leaves but not being so small that they are wafted off target by any winds. Conventional sprayers can also produce drops that have a similar average drop size. So, what’s the difference?
Well, the difference is the range of drop sizes produced. Conventional sprayers will have a much broader range of drop sizes; there will be some droplets that are much bigger than the 150-micron average desired size and some that are much smaller. CDA spraying confines almost all the spray volume to that 140–160-micron range, there are almost no bigger or smaller droplets. Big droplets tend to bounce or roll off leaves and smaller droplets tend to waft off target. This means that even though the average droplet sizes might be the same, the CDA spray, with its narrow spectrum of droplets, will be absorbed far more readily and stay on target better.
Up to an 80% reduction in glyphosate usage
The combination of the two factors means that CDA spraying can generally do the same job using only a fraction of the amount of herbicide used in conventional spraying. Almost all the glyphosate gets absorbed and so far, less is wasted. This means that the same weed killing power can be delivered by using often around 20% of the chemical that would be used through conventional sprayers.
These benefits are situational and CDA + ULV spraying should not be seen a universal way to reduce herbicide usage but, with applications like spraying to keep weeds down at amenity sites, or on paths or pavements then CDA + ULV spraying can dramatically reduce herbicide usage. This saves money and helps protect the environment.
