Enhanced crop nutrition strategy can reduce our dependence on pesticides

A well-balanced fertiliser programme will not only improve yield potential but will also help cut pesticide usage
A well-balanced fertiliser programme will not only improve yield potential but will also help cut pesticide usage
PJ Phelan

PJ Phelan

Farmers have very little influence over the renewal of pesticide approvals or of new pesticide registrations. In order to protect their survival and to enable them to achieve our national agricultural production targets, tillage farmers must:

  • Keep our politicians informed of the critical nature of herbicides and fungicides;
  • Take action to reduce their reliance on pesticides.

Disease control with fungicides is one of the major management tools that farmers use to protect yield potential. The withdrawal of approval of many products, and indeed the cost of finding replacement products, is putting that strategy under major stress.

Some of the withdrawals are due more to environmental concerns and pressure groups than to scientific fact. Farmers have very little influence on ­pressure groups.

But they can show and demonstrate that they are using the products that are available to them in a responsible manner and that they minimise their use where possible.

EU consumers need to be aware of the fact that all foods grown in Europe are highly regulated and that all pesticide usage must be recorded by farmers, and that those records are likely to be inspected at any time.

Consumers must also be made aware of the fact that 'Produced in Ireland' on a food label does not mean grown in Ireland and that logos with a tricolour does not mean grown in Ireland. In fact, those products may have come from any part of the world, possibly without any regulations on pesticide usage.

All pesticides must be used for identified reasons, with rates tailored to the specific task in hand.

The Integrated Pest Management programme, to which all farmers are signed up to, requires that a large range of crop management tools must be used before pesticides are used.

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Crop nutrition is one of the tools that farmers have to minimise pesticide application.

A well-balanced fertiliser programme will not alone improve yield potential but will also enable a reduction in pesticide usage. Nutrient ratios in soil are critical - excess of one nutrient can have adverse impacts on other nutrients resulting, among other impacts, in increased disease susceptibility.

The benefits of an appropriately balanced fertiliser programme in the reduction of disease pressures may be summarised as follows:


High levels of nitrogen, needed for high yields, are frequently associated with an increase in disease levels. That increase in disease is moderated by potassium, and may be either increased or decreased by phosphorus applications. High nitrogen usage increases the incidence of rust and mildew, but decreases the impacts of take-all.

Removal of residual nitrogen by growing an unfertilised catch crop prior to sowing potatoes, and then the use of ammonium rather than nitrate nitrogen can result in reduced potato scab.


High phosphorus levels adversely interact with several other nutrients and thereby have an indirect impact on disease severity. Take-all levels are increased by soil acidity and low soil P status. Incidentally, fresh lime application increases take-all levels. High P levels have been associated with increased septoria.


We had plenty of evidence this year of the benefits of high soil potassium levels for the susceptibility to drought. High potassium levels also decrease the incidence of most wheat diseases but has been associated with higher levels of both fusarium and take-all. In barley, high potassium levels have been linked with a reduction in both net blotch and mildew.


It is generally considered that when soil pH is satisfactory, calcium deficiency will not occur. In potatoes, soft rot, internal spotting and weak tuber skins are generally associated with calcium deficiency.


Adequate soil magnesium will reduce the impact of take-all in cereals and bacterial soft rot in potatoes.


Sulphur reduces mildew, rust and sharp eyespot in cereals, mildew in beet and light leaf spot in oilseed rape.


Manganese availability is linked to take-all, rust and mildew in cereals, and powdery scab in potatoes. Soil-applied manganese is rapidly immobilised in the ground; but with foliar applications being ineffective, it may be the only option in deficient soils.


Zinc deficiency increases the severity of rhizoctonia, fusarium and take-all in cereals. Zinc deficiency is also a health risk in animals and humans. Therefore, zinc application to cereals, where necessary, will provide a safe and effective method of increasing nutritive value.

In conclusion, plant nutrition is a useful tool to reduce our dependency on pesticides and may well provide more nutritive foods. The decision to apply any nutrients should be made following soil and possibly plant analysis. Start now and get a comprehensive soil analysis for each soil type, if not for each field, on your farm.

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

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