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Exercise 3: Systemic Fungicides
While protectant fungicides play an important role in the management of potato late blight, the
newer, systemic fungicides offer many advantages over the protectants. Instead of interacting
with the Phytophthora sporangia or zoospores on the surface of the leaf, the systemics penetrate
the leaf and stem tissues and suppress already established infections. Inside the host tissues,
the systemics are not as vulnerable to weathering by heavy rains as are the protectant fungicides
on the surface. Thus the intervals between sprays can be extended. Furthermore, the systemic
fungicides have biochemical modes of action that make them effective at doses far lower than those
required for the protectant fungicides.
Go back to the Potato menu to be sure that the Resistance level is set to "low."
Start the simulation again by clicking on Begin New in the Simulation menu. Advance to
July 12 by pressing the right arrow key on your keyboard, and in the Management menu, select
Spray Systemic....
Apply the spray at the default dose by clicking on the "Spray" button. (Note the dose of the systemic
fungicide compared to that of the protectant.) Advance 14 days, apply a second spray, and advance
to the end of the season. (Two sprays will be applied, one on July 13 and the other on July 27.)
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 "low resistance" cultivar sprayed with the protectant fungicide.
How do the costs of the systemic fungicide compare with those of the protectant fungicide? How does
the effectiveness of the systemic fungicide compare with that of the protectant fungicide? How does
the profitability of the systemic fungicide compare with that of the protectant fungicide? What are
the risks associated with the use of the systemic fungicide?
....proceed to EXERCISE 4
....return to Introduction
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