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Fungicide dose response curves

Understanding dose response curves

If a range of fungicide doses is applied to experimental field plots, levels of disease observed a few weeks later typically follow this pattern:


or the control can be represented graphically, see below:

How disease pressure and variety affect appropriate dose

Differing disease pressure is a major reason for varying appropriate doses between different crops. The diagrams below show dose-response curves, and the appropriate dose, for three crops, with contrasting levels of disease pressure.

High disease pressure, Susceptible variety Moderate disease pressure, Variety with moderate disease resistance
 Low disease pressure,
Resistant or immune variety
Weather conditions favourable to disease development Weather conditions less favourable to disease Weather conditions that prevent disease developement

Higher disease pressure and disease susceptibility justify higher inputs.

% control curves

When comparing treatments across sites or seasons it is useful to convert the disease curves to '%control' curves. This allows a better comparison, particularly when disease levels vary between sites or across seasons. Instead of a curve showing the level of disease declining with increasing fungicide dose, the curve shows the percentage control of disease as fungicide dose increases.

% disease % control

Interpreting dose response curves

At doses above the appropriate dose, profit is reduced by increased fungicide cost.
At doses below the appropriate dose, profit is seriously reduced by ineffective disease control.
Maximising profits may mean a small amount of disease remains in the crop despite treatment.

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