Understanding dose response curves Effect of disease pressure and variety
% control curves Interpreting 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:
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
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Low disease pressure,
Resistant or immune variety |
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| 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.
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 |
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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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