Basic information on primary and secondary apple scab infection periods

Weather data for Sanford ME. Forecast values begin October 17, 2008

    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 Apple Pest 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: Sunday, April 27 at 8 AM    --->     End: Wednesday, April 30 at 10 AM.
Growth stage at start of period: early Tight Clus.
Best guess is that this infection period accounts for 0.4 % of the season's total primary scab infection risk.

Infection period 2.
Begin: Monday, April 28 at 8 AM    --->     End: Thursday, May 01 at 7 AM.
Growth stage at start of period: Between Half Inch Green and Tight Cluster
Best guess is that this infection period accounts for 0.9 % of the season's total primary scab infection risk.

Infection period 3.
Begin: Saturday, May 03 at 8 AM    --->     End: Tuesday, May 06 at 11 AM.
Growth stage at start of period: Between Half Inch Green and Tight Cluster
Best guess is that this infection period accounts for 1 % of the season's total primary scab infection risk.

Wetting period following May 08, 2 AM rain was too short for scab infection.

Infection period 4.
Begin: Friday, May 16 at 8 PM    --->     End: Sunday, May 18 at 10 AM.
Growth stage at start of period: Between King Bloom and Full Bloom
Best guess is that this infection period accounts for 0.8 % of the season's total primary scab infection risk.

Wetting period following May 23, 5 PM rain was too short for scab infection.

Infection period 5.
Begin: Saturday, May 31 at 5 AM    --->     End: Monday, June 02 at 11 AM.
Growth stage at start of period: Fruit Set
Best guess is that this infection period accounts for 85 % of the season's total primary scab infection risk.

Infection period 6.
Begin: Tuesday, June 03 at 11 PM    --->     End: Saturday, June 07 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 0.6 % of the season's total primary scab infection risk.

Infection period 7.
Begin: Wednesday, June 04 at 7 AM    --->     End: Sunday, June 08 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 11 % of the season's total primary scab infection risk.

Infection period 8.
Begin: Tuesday, June 10 at 8 PM    --->     End: Thursday, June 12 at 9 AM.

The 13 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 9.
Begin: Saturday, June 14 at 8 PM    --->     End: Thursday, June 19 at 9 AM.

The 82 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 10.
Begin: Friday, June 20 at 2 PM    --->     End: Thursday, June 26 at 7 AM.

The 104 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 11.
Begin: Thursday, June 26 at 11 AM    --->     End: Tuesday, July 01 at 1 PM.

The 105 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 12.
Begin: Tuesday, July 01 at 3 PM    --->     End: Friday, July 04 at 2 PM.

The 56 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 13.
Begin: Thursday, July 03 at 5 PM    --->     End: Saturday, July 05 at 3 PM.

The 28 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 14.
Begin: Wednesday, July 09 at 2 PM    --->     End: Friday, July 11 at 9 AM.

The 19 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 15.
Begin: Monday, July 14 at 8 AM    --->     End: Tuesday, July 15 at 1 PM.

The 5 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 16.
Begin: Friday, July 18 at 12 PM    --->     End: Tuesday, July 22 at 5 PM.

The 93 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 17.
Begin: Saturday, July 19 at 4 PM    --->     End: Friday, July 25 at 2 PM.

The 128 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 18.
Begin: Wednesday, July 23 at 2 PM    --->     End: Saturday, July 26 at 11 AM.

The 48 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 19.
Begin: Sunday, July 27 at 2 AM    --->     End: Monday, July 28 at 3 PM.

Next infection period starts on same day, see next infection period for combined ratings.

Infection period 20.
Begin: Sunday, July 27 at 5 PM    --->     End: Tuesday, July 29 at 12 PM.

The 48 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 21.
Begin: Thursday, July 31 at 1 PM    --->     End: Friday, August 01 at 9 PM.

The 25 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 22.
Begin: Friday, August 01 at 11 PM    --->     End: Tuesday, August 05 at 12 PM.

The 61 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 23.
Begin: Wednesday, August 06 at 7 AM    --->     End: Tuesday, August 12 at 8 PM.

The 141 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 24.
Begin: Sunday, August 10 at 5 PM    --->     End: Wednesday, August 13 at 2 PM.

The 60 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 25.
Begin: Thursday, August 14 at 2 PM    --->     End: Sunday, August 17 at 12 PM.

The 52 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 26.
Begin: Saturday, August 16 at 5 AM    --->     End: Monday, August 18 at 1 PM.

The 33 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 27.
Begin: Tuesday, August 19 at 1 AM    --->     End: Wednesday, August 20 at 2 PM.

The 13 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 28.
Begin: Monday, August 25 at 9 AM    --->     End: Tuesday, August 26 at 2 PM.

The 5 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 29.
Begin: Saturday, September 06 at 5 AM    --->     End: Monday, September 08 at 1 PM.

The 37 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 30.
Begin: Tuesday, September 09 at 9 AM    --->     End: Thursday, September 11 at 2 PM.

The 34 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 31.
Begin: Friday, September 12 at 2 PM    --->     End: Monday, September 15 at 12 PM.

The 56 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 32.
Begin: Sunday, September 14 at 5 AM    --->     End: Tuesday, September 16 at 9 AM.

The 28 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 33.
Begin: Sunday, September 21 at 5 PM    --->     End: Tuesday, September 23 at 2 PM.

The 29 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.