Exercise 2: Protectant Fungicides
Where potato varieties susceptible to late blight are planted, the standard control practice is
to apply protectant fungicides at roughly weekly intervals, depending on the weather. During
periods of frequent rain, the interval between sprays may have to be shortened to 5 days, and
during dry weather, the interval may be extended to 10 days or more.
Go back to the Potato menu and reset the Resistance level to "low." Start the
simulation again by clicking on Begin New in the Simulation menu. Advance to
June 28 by pressing the right arrow key on your keyboard.
In the Management menu, select Spray Protectant...,
and apply the spray at the default dose by clicking on the "Spray" button. (Note that you make the
decision today to apply the spray tomorrow.) Advance 7 days and apply another spray, repeating
the process every 7 days 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.) Note the black line that represents the average residue
of the protectant fungicide on the leaves. The residue is high immediately following a spray, but it
quickly weathers away, especially with a heavy rain.
Again copy the economic report and paste it into the report with the previous results. Compare the
results of this run with those of the unsprayed "low resistance" cultivar.
How well did the protectant fungicide control the late blight epidemic? Weekly sprays are expensive,
both in the cost of the application and the cost of the fungicide itself. What effect did these
sprays have on the profitability of the crop? How does the profitability compare with
that of the highly resistant variety?
....proceed to EXERCISE 3
....return to Introduction
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