Exercise 4: Effects of Weather on Disease Development
The default weather conditions for this simulation are cool and wet, the conditions most favorable
for the development of late blight. In the Environment menu, click on Weather and select
"Hot and dry." Start the simulation with Begin New, and run it to the end of the season without
applying any fungicides. Copy the economic report and compare it with that of the unsprayed epidemic
under the cool, wet conditions.
Begin New and advance to June 28. Apply the protectant spray and repeat at 7-day intervals
for a total of 8 applications. (Sprays will be applied on June 29; July 6, 13, 20, and 27; and
August 3, 10, and 17.) Eight protectant sprays in hot, dry weather seems to be overkill. Let us
see if we can reduce the number of sprays to reduce the spray cost. Begin New and advance
to June 28. Apply the protectant spray and repeat at 10-day intervals for a total of 6 applications.
(Note: If you receive a warning that the spray will be applied in the rain, close the spray window
by clicking in its upper right corner, advance one day and attempt to spray again. Sprays will be
applied on June 29; July 9, 19, and 29; and August 9 and 19.) Compare the economic report with
that of the simulation applying 8 protectant sprays at 7-day intervals. Can we indeed reduce the spray
costs in hot, dry weather and still maintain profitable yields?
Again Begin New and advance to July 12. Apply two systemic sprays at 14-day intervals (July 13
and 27) and advance to the end of the season. Repeat the simulation with just one systemic spray.
Which is more profitable, one spray or two sprays of the systemic during hot, dry weather? How does the
profitability of two systemic sprays in hot, dry weather compare with that in cool, wet weather
(Exercise 3)?
....proceed to EXERCISE 5
....return to Introduction
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