How to calculate pesticide limits in aquatic buffer zones

A watercourse running through farmland

©Tim Scrivener

Since their introduction more than two decades ago, aquatic buffer zone rules when applying pesticides have become much more complex.

Here is our guide to what all growers and sprayer operators need to know to keep within the law and avoid prosecution or costly fines.

What is an aquatic buffer zone and why are they important?

It is a “no-spray” zone alongside a watercourse or ditch that limits spray reaching those areas. Aquatic buffer zones are important to protect insects, fish and plants from the risk of overspray from plant protection products.

See also: Avoid fines with grower guide to pesticide label changes

When were they introduced?

Six-metre aquatic buffer zones were in place in the early 1990s, but the original Local Environment Risk Assessment for Pesticides (Lerap) scheme was introduced on 29 March 1999 to provide more flexibility for pesticide users when applying products near watercourses.

Pesticide label changes

As products are re-registered, required buffer zones may change.

To help you keep up to date, Crops is working with Gatekeeper agronomists to highlight key changes and help you stay within the rules.

To subscribe to Crops go to or call 01444 475 632.

Do all pesticide products require a buffer zone?

No. Buffer zones are only stipulated where a potential risk to aquatic organisms has been identified for a particular product.

Which chemical classes/groups have the most risk?

It all depends on how toxic the product is to aquatic life and how the product is used – for example, at maximum application rate.

The tendency has been for insecticides to have aquatic buffer zones and those that present the most risk have usually been groups such as synthetic pyrethroids and organophosphates.

However, herbicides can also have aquatic buffer zones, due to their effects on non-target plants, and some fungicides now have them too.

How do I know if a product requires a buffer zone?

The product label will detail whether any aquatic buffer zone is required in the “precautions” section. You can also search the Pesticides Register database on the Health and Safety Executive (HSE) Pesticides website to find products that have an aquatic buffer zone requirement.

What is a Lerap?

There are three buffer zone schemes. The scheme designated to a product on its label will determine whether the buffer zone can be reduced.

Pesticide users can carry out a Lerap to determine – based on size of watercourse, the product’s dose rate and sprayer technology used – whether the buffer zone can be reduced.

For example, when using low-drift nozzles there is less risk of the pesticide reaching the watercourse, allowing the sprayer to work closer to the top of the bank.

A Lerap must be completed before each spraying operation by ground crop sprayers adjacent to watercourses, with the results recorded and kept for three years.

Does the size/type of watercourse or product dose rate make a difference?

Only when reducing the 5m buffer zone under the Lerap scheme and its interim extension.

Wider watercourses and lower dose rates are considered lower risk due to greater dilution of any pollution and, as a general rule, allow a reduction in the buffer.

Dry ditches only require a 1m buffer under all aquatic buffer zone schemes.

What if I am applying a complex mixture of products?

Then you must apply the aquatic buffer zone of the product that has the largest distance required.

What are the consequences/penalties for not adhering to aquatic buffer zone requirements?

Infringement of the statutory conditions of use may lead to enforcement action or financial penalties under CAP/Basic Payment Scheme if found by Rural Payments Agency (RPA) inspectors.

Always read the label carefully to ensure that you are clear about aquatic buffer zone requirements or check the Pesticides Register database for products with aquatic buffer zones before purchasing.

Why are there three schemes in operation?

The first scheme was introduced to allow users to reduce buffer zones on the basis of Lerap. It took a number of years to devise using the data available at the time.

Under modern risk assessments, several products were failing to demonstrate an acceptable risk with a 5m aquatic buffer zone.

t was not possible to issue authorisations with buffer zones greater than 5m at the time, so existing products were at risk of being withdrawn from the market and new products not authorised.

This meant that affected products were unavailable to users because the Lerap scheme was not sufficiently flexible, so changes were needed.

Subsequently, two supplementary schemes – Interim and Drift Reduction Technology – were introduced at the request of the chemical companies to address difficulties that would otherwise have precluded authorisations.

The priority at the time of introduction of these schemes was to find more flexible arrangements quickly and solve the immediate problems blocking authorisations.

Will the three schemes be intergrated?

The Health and Safety Executive (HSE) could have integrated the supplementary schemes as they developed. But it would have taken much longer, as these are crop- rather than product-specific.

In the future, though, the HSE would like to merge them. That process would also entail taking into account any new data or research since the schemes were introduced and to harmonise with other European member states as far as possible.

This will take some time to achieve, but the industry is making proposals to HSE to simplify the schemes.

Lerap A and B scheme

When the Lerap scheme was introduced in 1999, products with aquatic buffer zones were split into categories A and B.


Lerap A scheme diagram

Those categorised as Lerap A cannot have their buffer zone reduced under the Lerap scheme.

Common examples Mavrik (tau-fluvalinate), Dursban (chlorpyrifos).

Lerap B scheme diagram

Those categorised as Lerap B can have their buffer zone reduced under the Lerap scheme if this is justified under the circumstances of application. The product and the use with the most critical risk assessment drives the aquatic buffer zone required.

Common examples Bravo 500 (chlorothalonil), Adexar (epoxiconazole + fluxapyroxad).


Interim scheme


The interim scheme allows the product to have a buffer zone greater than 5m.

The interim scheme diagram

The distances can be 5m, which can be reduced to 1m by carrying out a Lerap.

Common examples Falcon (propaquizafop), Springbok (metazachlor + dimethanamid-P).

The interim scheme diagram

Products with buffer zone distances of 6-20m cannot have their aquatic buffer zone reduced. The distances are set for each crop, so a product can have more than one buffer zone distance.

Common examples Refinzar (penthiopyrad + picoxystrobin), Shirlan (fluazinam).


Drift reduction technology (DRT) scheme

DRT scheme diagram

The three-star DRT option requires appropriate technology (nozzles) to be used at all times up to 30m from watercourses. Permitted distances are fixed at 6m, 12m and 18m. The buffer zone distance is crop-specific so a product may have more than one.

Common examples Hurricane (diflufenican), Treoris (chlorothalonil + penthiopyrad).


With thanks to the HSE for help in compiling this article.