If you have water bodies near your fields, there are likely to be some restrictions on the way you can spray pre-emergence herbicides. These legal requirements are important to get right, so I’ve done my best to check the accuracy of this. Sorry that this is going to be a bit of a dull read, but I know of no way of making it more interesting. Apart from the picture of the cat.
The majority of pre-em products appear to be LERAP B rated, which means you have a choice: you can leave a 5 m no-spray zone (measured to the top of the bank of the watercourse) and then your extra legal obligations are met. If you want to reduce this down to 1 m, then you must spray at least the next 12 m swath with at least 3-star conditions, i.e. 0-1 m, no spray; 1 – 13 m, 3-star.
There is a smaller number of products that have 6 m no-spray zones or larger. You cannot reduce these. In particular, using a 4 star nozzle will not gain you anything extra (at the moment, anyway). Anything you do spray within 30 m of the water must be with at least 3-star conditions. My interpretation of this is that the 30 m 3-star zone is not in addition to the no-spray zone, but 30 m in total, i.e. 0 -6 m, no spray; 6 – 30 m, 3-star. If in doubt, check with the product manufacturer.
So how do you achieve a sensible 3-star treatment for soil-applied herbicides?
There are many, many ways to skin this cat (sorry Tigs, horrible phrase) and I am only
going to give you some simple examples. I will focus on predominantly vertical sprays, not angled or twin jets because, for the reasons outlined in earlier blogs, I think these will put the most spray in the right place.
There are no 3-star conditions with speeds greater than 12 km/h. Some of the earlier nozzles to be tested are limited to 10 or maybe even 8 km/h, but the most recent ones are all up to 12 km/h. So my examples are for nozzles that have this higher speed limit. Those of you who like to go faster will have to slow down to achieve 3-stars.
My aim is to find something that will give you 3-stars at 2 – 3 bar pressure. If you are slowing down just for the 3-star zone, then it is ok to let pressure drop down to 2 bar, but I wouldn’t recommend much lower.
There are a few nozzles that only achieve a star rating at a boom height less than 0.5 m. I have ignored all of these too – most of them are not relevant for arable boom spraying operations, but it is important to check maximum boom height if you are searching for something different.
Not all sizes of nozzle within a range have the same star rating, so you have to match the exact nozzle to the volume, pressure and speed and check that it has the 3-star rating on the CRD website. The CRD database is not hugely user-friendly, so I have done this for the following examples, based around 100 and 200 L/ha. Please note that this does not imply that these nozzles will give levels of weed control that is any better than other nozzles – we have not tested them – just that they meet your legal obligations. Remember the maximum boom height of 0.5 m too – this is crucial. And I haven't mentioned wind speed - all the normal rules apply and you must not spray in a higher wind speed than the Defra Code of Practice, even if you are using the highest level of drift reduction.
There are other nozzles available – and maybe the easiest place to start is our website page - https://www.ssau.co.uk/drift-reducing-nozzles - which has links to other sources of information, including the official CRD listing. But the ones I have selected have a reasonable pressure range, and a good range of sizes too, making it easy to get it right. In particular, the Teejet TTI retain three stars up to at least 5 bar, and the Lechler ID3 up to 8 bar, so by increasing pressure and reducing speed you can get a much wider range of volumes than I have given here. All three ranges include an ‘04’ size too, giving you even more flexibility.
Nozzle suggestions for 3-stars that can be achieved at 2-3 bar, 12 km/h and a 0.5 m boom height, which will deliver around 100 or 200 L/ha.
Boring disclaimer – while I have made every effort to check this, there could be mistakes in the above. You are responsible for your application.
Nozzle manufacturers also provide some useful information, but the definitive rule is that it must be on the CRD listing to comply with the rules. Be wary of information that states a nozzle gives a percentage drift reduction, or a JKI or other rating – these are not recognised in the UK, only the CRD star-rating meets the legal requirements.