Weedkillers protect crops and control grassland weeds, but they need to be kept out of water. Richard Simpson, from Kingshay Farming Trust, gives guidance.

Weedkillers, or herbicides, are valuable tools for producing home-grown forage, or maintaining productive grassland. Weeds reduce both quantity and quality of forage crops and may poison stock. Some weeds, such as ragwort, must be controlled by law.

Grassland weedkillers account for just 10% of the value of the UK crop protection market and, on average, lowland grassland is sprayed once every four or five years. Yet several herbicides, traditionally used on spring crops and grassland, are regularly found in water by environment agencies and water companies. While they may not threaten aquatic life, they can increase the cost of drinking water treatment.

The law

Herbicides are classed as "plant protection products" and legally defined as "pesticides". All products that control "pests" need an approval from the Pesticides Safety Directorate (PSD). This specifies what crops can be treated, application rates and safety precautions. All this is on the product label which users must follow. Additionally, the statutory Code of Practice for Using Plant Protection Products (www.pesticides.gov.uk) gives advice on best practice. Failure to comply can jeopardise single farm payments.

Training

Legal controls also apply to training pesticide users. Health and Safety at Work legislation requires all users to be trained and competent. However, for pesticides anyone born after the 31 December 1964, contracting (including helping a neighbour) or supervising an unqualified operator must hold an NPTC certificate of competence. The National Register of Sprayer Operators (NRoSO) has been set up by the Voluntary Initiative (VI). Almost 20,000 farmers and operators have now joined the scheme to benefit from regular refresher training.

Choosing weedkillers

Begin by identifying which weeds to control. To ensure correct identification and product choice, consult a BASIS-registered adviser who is up to speed with the latest recommendations and will know what is best for your particular situation. There should be one at your local merchant. The adviser should also provide a recommendation sheet on what and how much to use in each field. He can also advise on correct storage, local contractors and disposal.

Storage

Concentrated pesticides pose the greatest risk, so product storage needs to be up to scratch. However, it need not be complex or expensive. For instance, a chest freezer - correctly labelled, leakproof and locked - is a good solution for a small livestock farm. Pay particular attention to fire prevention, as tackling a pesticide store fire poses a major risk to water.

Buy only what is needed for each season. Each year check products held in store are still approved. Check approval status by asking a BASIS-registered adviser or use the pesticide register database at www.pesticides.gov.uk.

Check the sprayer

A correctly set up sprayer reduces the risk of pesticides reaching water and ensures it does a good job. Before the spraying season use clean water to check the sprayer is in good working order. Run the sprayer under pressure to check for drips and leaks.

Where necessary, tighten clips and replace damaged pipes and washers. Check there is a full, matching set of nozzles producing an even spray pattern across the boom. Use a one minute/30 second jug test to check nozzle flow rates are consistent. When variation between nozzles exceeds 10% replace the set. Check the pressure gauge - spraying at too high a pressure increases spray drift.

Most features can be independently checked by the National Sprayer Testing Scheme (NSTS). (See checklist at www.nsts.org.uk)

Filling, handling and disposal

Filling, handling and disposal practices are the most likely sources of pesticides reaching water from livestock farms.

Inspect the filling area identify where rainwater and any spills or run-off go. Farmyards often drain into a local stream or ditch, so it may be necessary to re-site the filling area or seal off drains. A drip tray, or portable bund, can be used underneath a sprayer when filling on grass, concrete or hardcore.

Alternatively, fill in a bunded concrete area where drainage is actively managed to stop pesticides reaching water, for example through a lined biobed. Ensure there is enough space to work in. Keep cat litter on hand to mop up spills. Never wash spills down the drain and take care to avoid tiny splashes when filling.

There is a strong risk of back-siphoning when filling, so use a bowser or separate storage tank and ensure the water supply is connected via a double check valve. Never take water direct from the mains, troughs or a river. Never leave a sprayer unattended while it is being filled.

Once empty, containers should be triple rinsed, allowed to drain and stored ready for professional disposal. Good disposal contractors will supply storage containers. Ask the contractor if different packaging materials need to be separated. Before moving to the field, check for drips and leaks, then set agitation to the minimum required (eg 200rpm pto speed) to avoid foaming while travelling.

Application

On the day, think through the spray operation. Check the recommendation sheet and the product label. Consider the conditions. Never spray when it is too windy, (Force 4 or more 10-15km/hour (6-9mph)), the ground is frozen or waterlogged or if heavy rain is forecast in the next few days. Identify an area of the field where the weed problem is less and leave untreated, so you can use it for leftover spray solution and/or sprayer washings.

In the field observe any label restrictions on spraying near water or hedges. Wherever practical, leave a 5m no-spray zone beside watercourses, hedges and neighbouring properties. With standard 110Á flat fan nozzles, keep boom height 40-50cm above the crop. On uneven ground boom height may need adjusting, but increasing boom height will increase drift.

After spraying, wash the sprayer down before deposits dry. Modern sprayers often have a clean water tank, hose and brush attached with internal nozzles to clean the tank. These make cleaning quick and easy in the field and may be available as a retrofit option. Failing this, the sprayer should be cleaned on grass well away from water. Focus external cleaning on the boom, back of the spray tank and rear tractor wheels. Always park the sprayer under cover to protect it from the elements and to ensure any remaining residues are not washed off.

Finally, be sure to record all spray applications. These will almost certainly be checked at cross-compliance or farm assurance inspections.

Contractors

A contractor can take a lot of hassle out of spraying, but the farmer is still responsible for ensuring he complies with the law. Be sure:

Contract spray operator holds the right NPTC certificate of competence and is a member of NRoSO

• Sprayer has current NSTS certificate
• Any filling point poses no risks to water
• Containers are cleaned and drained for disposal
• Agree who is responsible for disposal
• Accurate spray records are promptly supplied

What is a pesticide?

"Pesticide" is a broad definition within the Food and Environment Protection Act 1985 which includes herbicides, fungicides, insecticides, growth regulators, soil sterilants, rodenticides and wood preservatives among others.

Water quality standards

Stringent standards are set for water quality across Europe. Sophisticated monitoring can detect pesticide levels below one part in a billion - equivalent to one stem in 111,000 hay bales or one baked bean in 21m cans.

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