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Concerning amount of water pollution cases in 2019

Farmers are reminded to use best practice when applying herbicides, writes By Kieran Kenny, Teagasc Soils and Environment Adviser, Castlerea.

The Longford Central public water supply is one of 6 priority supplies in the country where exceedances for pesticides have been persistently detected in the drinking water.

In 2019, six samples were above the drinking water limit all due to the herbicide MCPA. 

Its supply is sourced from Lough Forbes with a large catchment bordering three counties, Longford, Leitrim and Roscommon that includes the towns/villages of Rooskey, Dromod, Mohill, Termonbarry, Newtownforbes, Drumlish, Ballinamuck and Bornacoola.

Since 2018, the catchment is part of a national monitoring programme for MCPA, involving intensive water sampling on a weekly and fortnightly basis from March to October and on a monthly basis for the winter period.

There are 18 sampling locations throughout the catchment on the Black River, Eslin River, Rinn River, parts of the Shannon, a few smaller streams and Lough Rinn.

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Sampling results

The results in 2019 were very concerning. The highest number of exceedances occurred in the April to June period with 13 sites above the limit on a few occasions.

At the end of September, after a short period of dry weather and increased herbicide applications, there was another spike in figures. Towards the end of the spraying season, three detections were found in October and one in November.

The four rounds of sampling throughout the winter period December to March have shown the catchment to be below the limit at all locations.

Unfortunately, with the commencement of this year’s spraying season, the most recent sample taken on 6th April found two MCPA exceedances on the Eslin River at Lough Erril Bridge and on the Black River at Breannskullew.

These series of results would indicate that residues of MCPA in the environment is not causing the problem, it is more likely due to poor practices by a small number of individuals.

What should farmers do?

The Department of Agriculture has continuously stated: that farmers should not feel compelled to use substances such as MCPA to tackle rush infestations:

“Provided there is evidence of agricultural activity (cutting/topping) or animals grazing – i.e. trampled vegetation or dung – in areas affected by rushes, farmers will not be penalised. Only areas that become overgrown in scrub as a result of being abandoned can be subject to penalties on inspection.”

New guidance from the Department on the control of rushes is based on minimising pesticide use by choosing a suitable control strategy of containment or suppression depending on the farm.

It suggests containment (topping and removal of rushes) is a more sustainable strategy then suppression for rush control where extensive farming is practiced on a poor sward, with poor soils, poor drainage, high rainfall and a high risk to watercourses.

Where your farm adviser indicates that Suppression is appropriate, frequent topping, improved soil fertility and good drainage will help limit rushes spreading. If chemical control is required, weed licking with Glyphosate is the safest option when water quality is a major concern.

If you choose to use MCPA then you must take precautions by following best practice:

  • The chemical MCPA cannot be used in a weed licker or knapsack sprayer;
  • Do not fill the sprayer from a watercourse;
  • Always read and follow the label instructions. Spray at the right rate and the right time: a young healthy growing crop and suitable weather conditions;
  • It cannot be sprayed within 5m of watercourses and dry drains;
  • Do not apply on waterlogged or poorly draining soils that slope steeply towards a water body or any other vulnerable area leading directly to surface or groundwater (eg karst). Another potential high-risk pathway is field drains filled towards the surface with stone. In this scenario, avoid band spraying within 5m of the drain;
  • Empty containers should be triple rinsed, and the rinse put into the sprayer. The tank washings must be sprayed in the field and not emptied in the farmyard;
  • Finally, the applicator must be a trained Professional Pesticide User and the equipment must be well maintained, regularly calibrated and tested every 3 years.
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