Advice for pesticide users: Safe herbicide use to protect drinking water

Drinking water monitoring results for Ireland show that a number of herbicides commonly used on grassland, such as MCPA, are being detected more frequently in recent years.

Careless storage, handling or use of pesticides can easily cause breaches of the legal limit for pesticides in drinking water. 

Rush control and MCPA Spraying rushes can very easily lead to breaches of the drinking water standard for pesticides, particularly if using MCPA products.

MCPA is water soluble and takes several weeks to break down. Rushes thrive in poorly drained areas (with a water table near the surface), which are prone to run-off to nearby water bodies.

Rush control tips:

* Use non-chemical control methods, e.g., cutting, drainage, sward 

* If spraying, target only the rush-affected areas; 

* Cut rushes one month before or one month after spraying to improve the effect of the spray; 

* Consider weed wiping with an appropriate herbicide as a rush control option.

How do herbicides get into drinking water?

There are two main sources: point sources (mainly in the farm or farmyard) – leaks from storage areas, or spills or drips from handling operations such as mixing, filling and washing; or, diffuse sources (mainly in the field) —inputs arising during or after application from processes such as spray drift, run-off and drainage.

Safeguard zones

Statutory ‘no-use’ zones (called safeguard zones) apply around drinking water abstraction points, ranging from 5m to 200m depending on the size of the supply.

Your local authority or the National Federation of Group Water Schemes can advise on this. 

Remember: a single drop of pesticide lost to a water body such as a typical stream (1m wide, 0.3m deep) can be enough to breach the legal limit for pesticides in drinking water of 0.1 part per billion along 30km of its length. 

* Always read and follow the product label; n Be aware of how near water bodies (ditches, streams, ponds, rivers, lakes, etc.) drains or wells are to where you are working; and 

* Find out if the treatment area is in the vicinity of a drinking water abstraction point or well.

Weeds in grassland:

Don’t underestimate the value of grassland husbandry such as lime, fertiliser, topping or reseeding as weed control measures. 

And remember that low levels of weeds really will not affect grass production and are beneficial to the environment.

Vigorously growing grass sward can out-compete weeds and prevent new weeds growing. While spraying at the right time doubles the effect of the spray

Herbicide DOs:

* DO read the product label instructions carefully and plan the treatment in advance, taking care to ensure strict compliance with the specified conditions of use.

* DO follow all health and safety 

* DO inform yourself of the location of all nearby water bodies (ditches, streams, ponds, rivers, lakes and springs). 

* DO find out if any groundwater body or surface water body in your locality is used as a drinking water source and, if so, the location of the nearest abstraction point. 

* DO ensure compliance with the safeguard (no-use) zones around drinking water abstraction points. 

* DO ensure that all of your pesticide products are stored in a secure, dry area, which cannot result in accidental leaks or spills. 

* Do ensure that all empty, triple-rinsed containers are disposed of in accordance with the Good Practice Guide for Empty Pesticide Containers. 

* DO ensure that application equipment is properly calibrated and in good working order. 

* DO take every precaution during mixing and preparation to avoid spills and drips. Minimise water volumes (rain and washings) on the handling area. 

* DO consider using drift-reducing nozzles if spraying. Keep the spray boom as low as possible to the ground and use the coarsest appropriate spray quality. 

* DO clean and wash down the sprayer at the end of the day, preferably in the field and well away from water bodies or open drains. 

* Tank washings should be sprayed onto the previously sprayed area, on a section far away from any water body, observing the maximum dose for that area. 

* DO maintain a distance of at least 10m, and preferably 50m, where possible.

Herbicide DON’Ts:

* DON’T perform handling operations (filling, mixing or washing the sprayer) near water bodies, open drains or well heads. 

* DON’T fill the sprayer directly from a water body. 

* DON’T spray if the grass is wet or if heavy rain is forecast within 48 hours after application. 

* DON’T spray during windy conditions. DON’T spray near open drains, wells or springs. 

* DON’T spray on waterlogged or poorly draining soils that slope steeply towards a water body, drain, well or on any other vulnerable area that leads directly to water. 

* DON’T discard sprayer washings down a drain or onto an area from which they can readily enter a water body.

Key messages Beware!

* Spraying rushes can very easily lead to breaches of the drinking water standard for pesticides, particularly if using MCPA. 

* All MCPA products for rush control have a 5m buffer zone from watercourses (this includes any dry drains that could hold water). n MCPA products cannot be used in weed lickers. 

* All MCPA containers should be triple rinsed after use with the rinse put into the sprayer. Mechanical control should be the first option and then spray the regrowth and target only the rush-affected areas. 

* One drop of herbicide can breach drinking water limits in a small stream for 30km. 

* Do not fill sprayers from watercourses. 

* Ensure that the sprayer operator is aware of any drinking water abstraction points or wells in the local area (5-200m safeguard zones.


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