Basic information on primary and secondary apple scab infection periods

Background Information for this page

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Weather data for Greenville RI.  Forecast values begin May 22, 2012

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: Wednesday, March 28 at 11 AM    --->     End: Saturday, March 31 at 11 PM.        Growth stage at start of period:  Between Half Inch Green and Tight Cluster       Best guess is that this infection period accounts for 0.6 % of the season's total primary scab infection risk.

Wetting period following  March 31, 3 AM rain was too short for scab infection.

Wetting period following  April 01, 5 PM rain was too short for scab infection.

Infection period  2.       Begin: Thursday, April 12 at 11 AM    --->     End: Sunday, April 15 at 9 AM.        Growth stage at start of period:  Between Tight Cluster and Open Cluster       Best guess is that this infection period accounts for 2 % of the season's total primary scab infection risk.

Wetting period following  April 15, 2 AM rain was too short for scab infection.

Infection period  3.       Begin: Saturday, April 21 at 2 AM    --->     End: Tuesday, April 24 at 7 AM.        Growth stage at start of period:  Between Full Bloom and Petal Fall       Best guess is that this infection period accounts for less than 0.1 % of the season's total primary scab infection risk.

Infection period  4.       Begin: Sunday, April 22 at 11 AM    --->     End: Thursday, April 26 at 3 AM.        Growth stage at start of period:  Between Full Bloom and Petal Fall       Best guess is that this infection period accounts for 72 % of the season's total primary scab infection risk.

Wetting period following  April 27, 2 AM rain was too short for scab infection.

Infection period  5.       Begin: Tuesday, May 01 at 2 AM    --->     End: Sunday, May 06 at 2 PM.        Growth stage at start of period:  1 - 5 days after Petal Fall       Best guess is that this infection period accounts for 15 % of the season's total primary scab infection risk.

Infection period  6.       Begin: Thursday, May 03 at 2 AM    --->     End: Tuesday, May 08 at 3 PM.        Growth stage at start of period:  6 or more days after Petal Fall       Best guess is that this infection period accounts for 0.7 % of the season's total primary scab infection risk.

Infection period  7.       Begin: Tuesday, May 08 at 2 AM    --->     End: Thursday, May 10 at 4 PM.        Growth stage at start of period:  6 or more days after Petal Fall       Next infection period starts on same day, see next infection period for combined ratings.

Infection period  8.       Begin: Tuesday, May 08 at 6 PM    --->     End: Saturday, May 12 at 12 PM.        Growth stage at start of period:  6 or more days after Petal Fall       Best guess is that this infection period accounts for 8 % of the season's total primary scab infection risk.

Infection period  9.       Begin: Tuesday, May 15 at 2 PM    --->     End: Saturday, May 19 at 7 AM.        Growth stage at start of period:  6 or more days after Petal Fall       Best guess is that this infection period accounts for 2 % of the season's total primary scab infection risk.

Infection period  10.       Begin: Monday, May 21 at 2 PM    --->     End: Friday, May 25 at 12 PM.               The 47 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.