Basic information on primary and secondary apple scab infection periods

Weather data for Greenville RI. Forecast values begin September 2, 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: Monday, April 28 at 7 AM    --->     End: Thursday, May 01 at 1 AM.
Growth stage at start of period: Between Open Cluster and Full Pink
Best guess is that this infection period accounts for 6 % of the season's total primary scab infection risk.

Infection period 2.
Begin: Friday, May 02 at 2 AM    --->     End: Monday, May 05 at 1 PM.
Growth stage at start of period: Between Full Pink and King Bloom
Best guess is that this infection period accounts for 1 % of the season's total primary scab infection risk.

Infection period 3.
Begin: Saturday, May 03 at 8 PM    --->     End: Tuesday, May 06 at 10 AM.
Growth stage at start of period: Between Full Pink and King Bloom
Best guess is that this infection period accounts for 3 % of the season's total primary scab infection risk.

Infection period 4.
Begin: Thursday, May 08 at 2 AM    --->     End: Saturday, May 10 at 12 PM.
Growth stage at start of period: Between Full Bloom and Petal Fall
Best guess is that this infection period accounts for 14 % of the season's total primary scab infection risk.

Infection period 5.
Begin: Friday, May 09 at 8 AM    --->     End: Sunday, May 11 at 9 AM.
Growth stage at start of period: Between Full Bloom and Petal Fall
Best guess is that this infection period accounts for 9 % of the season's total primary scab infection risk.

Infection period 6.
Begin: Friday, May 16 at 2 PM    --->     End: Sunday, May 18 at 10 AM.
Growth stage at start of period: 1 - 5 days after Petal Fall
Best guess is that this infection period accounts for 32 % of the season's total primary scab infection risk.

Infection period 7.
Begin: Sunday, May 18 at 4 PM    --->     End: Tuesday, May 20 at 7 AM.
Growth stage at start of period: Fruit Set
Best guess is that this infection period accounts for 5 % of the season's total primary scab infection risk.

Infection period 8.
Begin: Tuesday, May 20 at 5 PM    --->     End: Thursday, May 22 at 9 AM.
Growth stage at start of period: 6 or more days after Petal Fall
Best guess is that this infection period accounts for 4 % of the season's total primary scab infection risk.

Wetting period following May 22, 3 PM rain was too short for scab infection.

Infection period 9.
Begin: Tuesday, May 27 at 4 AM    --->     End: Wednesday, May 28 at 6 AM.
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 10.
Begin: Tuesday, May 27 at 5 PM    --->     End: Thursday, May 29 at 3 AM.
Growth stage at start of period: 6 or more days after Petal Fall
Best guess is that this infection period accounts for 19 % of the season's total primary scab infection risk.

Infection period 11.
Begin: Saturday, May 31 at 5 PM    --->     End: Monday, June 02 at 10 AM.
Growth stage at start of period: 6 or more days after Petal Fall
Best guess is that this infection period accounts for 3 % of the season's total primary scab infection risk.

Infection period 12.
Begin: Wednesday, June 04 at 5 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 4 % of the season's total primary scab infection risk.

Infection period 13.
Begin: Sunday, June 15 at 6 AM    --->     End: Thursday, June 19 at 1 PM.

The 83 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 14.
Begin: Wednesday, June 18 at 5 PM    --->     End: Friday, June 20 at 10 AM.

The 17 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 15.
Begin: Friday, June 20 at 8 PM    --->     End: Sunday, June 22 at 2 PM.

The 21 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 16.
Begin: Sunday, June 22 at 8 PM    --->     End: Thursday, June 26 at 8 AM.

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

Infection period 17.
Begin: Sunday, June 29 at 12 AM    --->     End: Monday, June 30 at 3 PM.

The 21 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 18.
Begin: Monday, June 30 at 3 AM    --->     End: Tuesday, July 01 at 12 PM.

The 9 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 19.
Begin: Wednesday, July 02 at 10 AM    --->     End: Friday, July 04 at 7 PM.

The 31 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 20.
Begin: Friday, July 04 at 12 AM    --->     End: Sunday, July 06 at 3 PM.

The 53 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 21.
Begin: Saturday, July 05 at 2 AM    --->     End: Monday, July 07 at 2 PM.

The 44 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 22.
Begin: Monday, July 14 at 9 AM    --->     End: Tuesday, July 15 at 12 PM.

The 3 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 23.
Begin: Friday, July 18 at 8 PM    --->     End: Sunday, July 20 at 9 AM.

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

Infection period 24.
Begin: Sunday, July 20 at 11 PM    --->     End: Friday, July 25 at 2 PM.

The 99 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 25.
Begin: Tuesday, July 22 at 7 PM    --->     End: Saturday, July 26 at 11 AM.

The 64 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 26.
Begin: Sunday, July 27 at 2 AM    --->     End: Tuesday, July 29 at 11 AM.

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

Infection period 27.
Begin: Thursday, July 31 at 2 AM    --->     End: Friday, August 01 at 1 PM.

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

Infection period 28.
Begin: Thursday, July 31 at 6 PM    --->     End: Saturday, August 02 at 10 AM.

The 42 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 29.
Begin: Saturday, August 02 at 2 PM    --->     End: Monday, August 04 at 8 PM.

The 41 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 30.
Begin: Monday, August 04 at 2 PM    --->     End: Tuesday, August 05 at 5 PM.

The 3 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 31.
Begin: Wednesday, August 06 at 2 AM    --->     End: Sunday, August 10 at 1 PM.

The 84 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 32.
Begin: Monday, August 11 at 2 AM    --->     End: Saturday, August 16 at 3 PM.

The 108 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 33.
Begin: Thursday, August 14 at 2 PM    --->     End: Sunday, August 17 at 12 PM.

The 44 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 34.
Begin: Tuesday, August 19 at 11 AM    --->     End: Wednesday, August 20 at 10 PM.

The 11 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.

Infection period 35.
Begin: Saturday, August 30 at 5 AM    --->     End: Monday, September 01 at 9 AM.

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

Infection period 36.
Begin: Saturday, September 06 at 7 AM    --->     End: Tuesday, September 09 at 3 PM.

The 69 hours of rain and leaf wetness during this period provided conditions for conidial (secondary) scab infection.