A calendar spray program of weekly fungicide applications is very conservative and tends to over-control
apple scab during dry seasons when there are fewer infection periods. Another strategy is to monitor
infection periods and apply a fungicide with good after-infection activity within 3-4 days after the
start of an identified infection period. During wet seasons, this strategy may not offer much of an
advantage over a calendar spray program, although sometimes two or more infection periods can be covered
with a single spray. However, during dry seasons, the after-infection approach should enable a grower
to reduce the number of sprays and therefore reduce the scab control costs.
As in Exercise 1, run the simulation with the default values for cultivar susceptibility, weather, and
inoculum (highly susceptible cultivar, moderate temperatures and moderate rainfall, and
1010 ascospores). In the Simulation menu, select Begin New to start
a new simulation. In the View menu, turn on the graphing of the Eradican Residue and
of the Infection Period.
Advance through time as before, but this time apply an Eradican spray within 3-4 days after an infection
period has been identified. (The infection period "flags" appear as a short, vertical, light blue lines
about mid way up the graph.) Because of the rains, it may not be possible to apply a spray within 4 days
of an infection period, but there is still some after-infection activity even 5-6 days after an infection.
Note that a few infection periods occur on days without rain. This is the result of leaf wetness caused
by fog or dew. Continue to the end of the season and copy and paste the economic report into the
document that you started in Exercise 1.
As with the Protectan exercise, repeat the Eradican sprays using the weather conditions of moderate
temperatures and low rainfall (dry). As before, copy and paste the economic report into your document.
What are the advantages of an after-infection spray program? What are its drawbacks?
