Farm Ireland

Sunday 20 January 2019

Some simple steps can take the stress out of the spraying season

Make sure you have last year's pesticide records finalised
Make sure you have last year's pesticide records finalised
PJ Phelan

PJ Phelan

We have another spraying season about to commence so it is time to ensure that any mistakes made last season are not repeated this year. First to the simple things:

  • Your sprayer must be either less than five years old or have passed a Department approved sprayer test. If your sprayer is not in test you must have it tested. A full list of approved testers is available at
  • The sprayer operator must have completed a sprayer training course and must have a Pesticide User Number(PU). There are still some farmers who have completed the training and have not applied for their PU number. To do so simply log into or contact your consultant/advisor.
  • Make sure you have last year's pesticide records finalised.
  • All empty pesticide containers should be triple rinsed, punctured and flattened before disposal.

Check any notes you may have on efficacy of last year's pesticide applications and review what may have caused any deficiencies in control levels.

Failure of pesticides to give a satisfactory level of control can be due to either the pesticide or the operator.

The pesticide. We still have a wide enough range of pesticides, which when combined with cultural controls, will control all our main weeds, diseases and insect pests. Selection and timing of the most appropriate pesticide is still one of our major challenges.

Limited stock ranges by individual merchants is a problem but most merchants will source most products if given adequate notice . Try to place your orders at least one week in advance of expected spraying date.

Resistance development by individual weeds, diseases and insect pests to pesticides has escalated at an alarming rate in recent years.

The onus is very much on agronomists and farmers to ensure that they adopt the recommended practices to minimise resistance development.

Use of pesticides with different modes of action and avoiding using the same active ingredients in sequence are common practice. However, while you might be adding one or two litres of pesticide to 150/200 litres of water very little thought is given to the quality of water being used.

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Many pesticides are most effective when the pH of the spray solution is between 5 and 6. Pesticides such as glyphosate, dicamba and 2,4-D are weak acids as they have a negative charge. Negatively charged anions attach to positively charged cations such as calcium and magnesium.

Water with a high pH due to a high level of bicarbonate (calcium and magnesium) has an impact on the efficacy of many pesticides. Most, if not all of the generic formulations, of glyphosate degrade very rapidly in the presence of bicarbonates.

The addition of a pH conditioner such as Spray Plus Li 700 or X-Change will inactivate the bicarbonates and allow the pesticide to work. Many farmers will remember adding ammonium sulphate in the distant past to Roundup - that would have done a similar job.

There are suggestions that up to 85-90pc of our pesticides will work better when pH conditioners are used when the spray water used is high in bicarbonates. The cost of the pH conditioners can be as little as €0.25 - €0.45 per acre.

A range of water used for spraying in the Thurles area gave bicarbonate contents as outlined in the table below.

The addition of a water conditioner should be strongly considered for each of the "tap", "spring" and "river" sources analysed. The rainwater samples do not need a water conditioner despite the fact that the pH of one of them was 7.2. High pH may indicate a high level of bicarbonates but that is not necessarily the case.

Without doubt there are many areas of the country and perhaps the county where bicarbonate content of "tap", "spring" and "river" sources are low. Your first step should therefore be to have your spraying water analysed for bicarbonate and following that discuss with your agronomist if a water conditioner might be of benefit.

PJ Phelan is a tillage advisor based in Tipperary and is a member of the ACA and ITCA

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