Apple scab: primary infection period details

Scab Infection Period Details

Background Information for this page

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Weather data for Sanford ME.  Forecast values begin May 17, 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 evaluated with the Jones revision of the Mills table.     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 time and end time.     The estimates shown below should only be used as supplements to on-site observations.      Postinfection time limit for sterol inhibitor or strobilurin fungicides is capped at 72 hours maximum to reduce the chance of selecting for resistant strains of scab.  Application of these fungicides up to 96 hours or more after the start of an infection period may still provide control, but at increasing risk of resistant scab selection.

******   Primary  Infection  Period  1  Details   ******     Begin: Sunday, March 25 at 2 AM    --->     Last rain hour: Sunday, March 25 at 3 PM.         Growth stage at start of period:  Half-inch Green    This infection period accounts for less than 1% of the year's total primary scab risk.           Approximately 0.18 inch rain and 32 leaf wet hours, with 41 F degrees average temperature during wet hours.      Cumulative scab ascospore release by end of this wetting period is roughly 1%.

This infection period accompanied by daytime rain to release ascospores.     Opportunity for surface fungicide kickback ends No infection periodCounting from beginning of daytime ascospore release (low inoculum blocks), opportunity for surface fungicide kickback ends Tuesday, March 27, at 8 AM.         Opportunity for sterol inhibitor or strobilurin kickback ends No infection period   Counting from beginning of daytime ascospore release (low inoculum blocks), kickback window ends Wednesday, March 28, at 8 AM.         First generation lesions arising from this infection period would start appearing by Saturday, January 0.

Wetting period following  Wednesday, March 28, 5 PM rain was too short for scab infection.      Approximately 0.01 inch rain and 3 leaf wet hours, with 43 F degrees average temperature during wet hours.        Cumulative scab ascospore release by end of this wetting period is roughly 1%.

Wetting period following  Sunday, April 01, 8 PM rain was too short for scab infection.      Approximately 0.11 inch rain and 15 leaf wet hours, with 38 F degrees average temperature during wet hours.        Cumulative scab ascospore release by end of this wetting period is roughly 1%.

Wetting period following  Sunday, April 08, 8 PM rain was too short for scab infection.      Approximately 0.03 inch rain and 11 leaf wet hours, with 40 F degrees average temperature during wet hours.        Cumulative scab ascospore release by end of this wetting period is roughly 2%.

******   Primary  Infection  Period  2  Details   ******     Begin: Wednesday, April 11 at 8 PM    --->     Last rain hour: Thursday, April 12 at 11 PM.             Growth stage at start of period:  Between Half Inch Green and Tight Cluster        This infection period accounts for less than 1% of the year's total primary scab risk.               Approximately 0.07 inch rain and 30 leaf wet hours, with 40 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 2%.        Reliable pre-infection protection during this period expected if full dose + good coverage captan or EBDC fungicide applied since Wednesday, April 4, 6 AM, or if strobilurin fungicide applied since Friday, April 6, 6 AM.

Wetting period long enough only for ascospores released at night.          Opportunity for surface fungicide kickback ends Friday, April 13, at 2 PM.              Opportunity for sterol inhibitor or strobilurin fungicide kickback ends Saturday, April 14, at 8 PM.              First generation lesions arising from this infection period would start appearing by Monday, April 30.          If conidia from 1st generation lesions spread infection, 2nd generation lesions could show as early as Tuesday, May 15.

Wetting period following  Thursday, April 12, 7 PM rain was too short for scab infection.      Approximately 0.10 inch rain and 15 leaf wet hours, with 38 F degrees average temperature during wet hours.        Cumulative scab ascospore release by end of this wetting period is roughly 2%.

******   Primary  Infection  Period  3  Details   ******     Begin: Sunday, April 22 at 2 AM    --->     Last rain hour: Monday, April 23 at 9 PM.             Growth stage at start of period:  Between King Bloom and Full Bloom        This infection period accounts for roughly 27% of the year's total primary scab risk.               Approximately 2.98 inch rain and 56 leaf wet hours, with 47 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 33%.        Reliable protection if strobilurin fungicide was applied since Wednesday, April 18, 6 AM. But over 2 inches rain during infection period caused captan or EBDC coverage depletion before end of infection period.  In this case, a fungicide with post-infection activity should be used as soon as possible.

This infection period accompanied by daytime rain to release ascospores.          Opportunity for surface fungicide kickback ends Monday, April 23, at 4 PM.   Counting from beginning of daytime ascospore release (low inoculum blocks), opportunity for surface fungicide kickback ends Monday, April 23, at 9 PM.              Opportunity for sterol inhibitor or strobilurin kickback ends Wednesday, April 25, at 2 AM.   Counting from beginning of daytime ascospore release (low inoculum blocks), kickback window ends Wednesday, April 25, at 8 AM.              First generation lesions arising from this infection period would start appearing by Friday, May 11.          If conidia from 1st generation lesions spread infection, 2nd generation lesions could show as early as Friday, May 25.

******   Primary  Infection  Period  4  Details   ******     Begin: Thursday, April 26 at 6 PM    --->     Last rain hour: Friday, April 27 at 10 AM.             Growth stage at start of period:  Between King Bloom and Full Bloom        This infection period accounts for less than 1% of the year's total primary scab risk.               Approximately 0.41 inch rain and 17 leaf wet hours, with 47 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 35%.               Reliable pre-infection protection during this period expected if full dose + good coverage captan or EBDC fungicide applied since Monday, April 23, 6 AM, or if strobilurin fungicide applied since Saturday, April 21, 6 AM.

Wetting period long enough only for ascospores released at night.          Opportunity for surface fungicide kickback ends Saturday, April 28, at 2 PM.              Opportunity for sterol inhibitor or strobilurin fungicide kickback ends Sunday, April 29, at 6 PM.              First generation lesions arising from this infection period would start appearing by Monday, May 14.          If conidia from 1st generation lesions spread infection, 2nd generation lesions could show as early as Saturday, May 26.

******   Primary  Infection  Period  5  Details   ******     Begin: Tuesday, May 1 at 3 AM    --->     Last rain hour: Saturday, May 5 at 4 AM.             Growth stage at start of period:  Between Full Bloom and Petal Fall        This infection period accounts for roughly 30% of the year's total primary scab risk.               Approximately 1.02 inch rain and 116 leaf wet hours, with 47 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 63%.        Reliable pre-infection protection during this period expected if full dose + good coverage captan or EBDC fungicide applied since Thursday, April 26, 6 AM, or if strobilurin fungicide applied since Saturday, April 28, 6 AM.

This infection period accompanied by daytime rain to release ascospores.          Opportunity for surface fungicide kickback ends Wednesday, May 2, at 10 PM.   Counting from beginning of daytime ascospore release (low inoculum blocks), opportunity for surface fungicide kickback ends Thursday, May 3, at 3 AM.              Opportunity for sterol inhibitor or strobilurin kickback ends Friday, May 4, at 3 AM.   Counting from beginning of daytime ascospore release (low inoculum blocks), kickback window ends Friday, May 4, at 8 AM.              First generation lesions arising from this infection period would start appearing by Thursday, May 17.          If conidia from 1st generation lesions spread infection, 2nd generation lesions could show as early as Saturday, June 2.

******   Primary  Infection  Period  6  Details   ******     Begin: Tuesday, May 8 at 5 AM    --->     Last rain hour: Thursday, May 10 at 10 PM.             Growth stage at start of period:  Between Full Bloom and Petal Fall        This infection period accounts for roughly 30% of the year's total primary scab risk.               Approximately 1.86 inch rain and 74 leaf wet hours, with 52 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 91%.               Reliable pre-infection protection during this period expected if full dose + good coverage captan or EBDC fungicide applied since Saturday, May 5, 6 AM, or if strobilurin fungicide applied since Friday, May 4, 6 AM.

This infection period accompanied by daytime rain to release ascospores.          Opportunity for surface fungicide kickback ends Wednesday, May 9, at 10 AM.   Counting from beginning of daytime ascospore release (low inoculum blocks), opportunity for surface fungicide kickback ends Wednesday, May 9, at 12 PM.              Opportunity for sterol inhibitor or strobilurin kickback ends Friday, May 11, at 5 AM.   Counting from beginning of daytime ascospore release (low inoculum blocks), kickback window ends Friday, May 11, at 8 AM.              First generation lesions arising from this infection period would start appearing by Monday, May 21.

******   Primary  Infection  Period  7  Details   ******     Begin: Monday, May 14 at 8 AM    --->     Last rain hour: Thursday, May 17 at 3 AM.             Growth stage at start of period:  1 - 5 days after Petal Fall        This infection period accounts for roughly 7% of the year's total primary scab risk.               Approximately 0.39 inch rain and 68 leaf wet hours, with 59 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 97%.        Reliable pre-infection protection during this period expected if full dose + good coverage captan or EBDC fungicide applied since Thursday, May 10, 6 AM, or if strobilurin fungicide applied since Friday, May 11, 6 AM.

This infection period accompanied by daytime rain to release ascospores.          Opportunity for surface fungicide kickback ends Tuesday, May 15, at 5 AM.              Opportunity for sterol inhibitor or strobilurin fungicide kickback ends Thursday, May 17, at 8 AM.              First generation lesions arising from this infection period would start appearing by Saturday, May 26.

******   Primary  Infection  Period  8  Details   ******     Begin: Tuesday, May 15 at 4 PM    --->     Last rain hour: Thursday, May 17 at 3 AM.             Growth stage at start of period:  Fruit Set        This infection period accounts for roughly 1% of the year's total primary scab risk.               Approximately 0.78 inch rain and 40 leaf wet hours, with 60 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 98%.               Reliable pre-infection protection during this period expected if full dose + good coverage captan or EBDC fungicide applied since Thursday, May 10, 6 AM, or if strobilurin fungicide applied since Friday, May 11, 6 AM.

This infection period accompanied by daytime rain to release ascospores.          Opportunity for surface fungicide kickback ends Wednesday, May 16, at 11 AM.              Opportunity for sterol inhibitor or strobilurin fungicide kickback ends Friday, May 18, at 4 PM.              First generation lesions arising from this infection period would start appearing by Sunday, May 27.