Basic information on primary and secondary apple scab infection periods

Background Information for this page

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Weather data for Middletown RI.  Forecast values begin May 21, 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 12 PM    --->     End: Sunday, April 01 at 1 PM.        Growth stage at start of period:  Between Green Tip and Quarter Inch Green       Best guess is that this infection period accounts for 0.1 % of the season's total primary scab infection risk.

Infection period  2.       Begin: Saturday, March 31 at 5 AM    --->     End: Monday, April 02 at 5 PM.        Growth stage at start of period:  Between Half Inch Green and Tight Cluster       Best guess is that this infection period accounts for 0.1 % of the season's total primary scab infection risk.

Wetting period following  April 01, 6 PM rain was too short for scab infection.

Infection period  3.       Begin: Thursday, April 12 at 2 PM    --->     End: Sunday, April 15 at 2 PM.        Growth stage at start of period:  Between Half Inch Green and Tight Cluster       Best guess is that this infection period accounts for 0.8 % of the season's total primary scab infection risk.

Infection period  4.       Begin: Sunday, April 15 at 2 AM    --->     End: Tuesday, April 17 at 12 PM.        Growth stage at start of period:  Open Cluster       Best guess is that this infection period accounts for less than 0.1 % of the season's total primary scab infection risk.

Infection period  5.       Begin: Sunday, April 22 at 11 AM    --->     End: Thursday, April 26 at 4 AM.        Growth stage at start of period:  Between Full Pink and King Bloom       Best guess is that this infection period accounts for 51 % of the season's total primary scab infection risk.

Infection period  6.       Begin: Tuesday, May 01 at 4 AM    --->     End: Sunday, May 06 at 3 PM.        Growth stage at start of period:  Between Full Bloom and Petal Fall       Best guess is that this infection period accounts for 25 % of the season's total primary scab infection risk.

Infection period  7.       Begin: Thursday, May 03 at 3 AM    --->     End: Monday, May 07 at 11 AM.        Growth stage at start of period:  Between Full Bloom and Petal Fall       Best guess is that this infection period accounts for 0.4 % of the season's total primary scab infection risk.

Infection period  8.       Begin: Tuesday, May 08 at 11 PM    --->     End: Saturday, May 12 at 1 PM.        Growth stage at start of period:  95% Petal Fall       Best guess is that this infection period accounts for 17 % of the season's total primary scab infection risk.

Infection period  9.       Begin: Tuesday, May 15 at 2 PM    --->     End: Friday, May 18 at 11 AM.        Growth stage at start of period:  6 or more days after Petal Fall       Best guess is that this infection period accounts for 5 % of the season's total primary scab infection risk.

Infection period  10.       Begin: Monday, May 21 at 2 PM    --->     End: Friday, May 25 at 11 AM.               The 46 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.