Basic information on primary and secondary apple scab infection periods

Background Information for this page

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Weather data for Sanford ME.  Forecast values begin May 18, 2013

Each expected ascospore release is tracked as a separate event.  Infection periods representing separate ascospore releases can overlap.  Growers counting infection periods for the Delayed First-Spray Strategy can consider infection periods separated by less than 24 hours of dry leaves as a single prolonged infection period, as described in the New England Tree Fruit Management Guide.  Wetting period duration is compared against the Revised MillsTable by MacHardy et al. for daytime rains during the primary scab season (release of ascospores).  Wetting period duration for night-only rains during primary scab season, and after the completion of ascospore maturation (secondary scab season) are evaluated with the Jones revision of the Mills table.      The increase in natural resistance to scab infection in the weeks after petal fall is not factored into the Mills table.  Because of this, some of the summer wetting periods rated as scab infection periods may in fact have been too sort to cause late season infections.  Dry hours in middle of a wet period are not counted toward duration of the wet period.  As a result, wetting period duration is not simply the difference between start and end times.      The estimates shown below should only be used as supplements to on-site observations.

Infection period  1.       Begin: Saturday, May 11 at 5 AM    --->     End: Tuesday, May 14 at 1 PM.               The 33 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period  2.       Begin: Wednesday, May 15 at 4 PM    --->     End: Saturday, May 18 at 8 AM.               The 17 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period  3.       Begin: Monday, May 20 at 1 PM    --->     End: Thursday, May 30 at 12 AM.               The 174 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.