Exercise 5: Disease Management with Disease Thresholds
With slowly evolving epidemics, it is possible to let the disease develop until it has reached a certain
threshold level before beginning the spray program. Let us try this with late blight, using the first
visible symptoms as our threshold.
Set the potato variety to low resistance and the weather to cool and wet and begin the simulation again.
Advance the time until you see the brown line representing foliage blighted just beginning to appear above
the baseline. (Imagine you are walking the field, looking for the first lesions to appear on the lower
leaves.) Start a protectant spray program using intervals of 5-7 days. Compare your results with
those of the protectant spray program begun on June 29.
Repeat the simulation using the systemic fungicide applied at intervals of 7-10 days. Compare your
results with those of the systemic spray program begun on July 13.
Is it feasible to use a disease threshold for controlling late blight? (Explain.)
....proceed to EXERCISE 6
....return to Introduction
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