Apple scab: primary infection period details

Scab Infection Period Details

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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 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: Wednesday, March 28 at 11 AM    --->     Last rain hour: Saturday, March 31 at 1 PM.         Growth stage at start of period:  Between Half Inch Green and Tight Cluster    This infection period accounts for roughly 1% of the year's total primary scab risk.           Approximately 0.19 inch rain and 40 leaf wet hours, with 44 F degrees average temperature during wet hours.      Cumulative scab ascospore release by end of this wetting period is roughly 3%.    Reliable pre-infection protection during this period expected if full dose + good coverage captan or EBDC fungicide applied since Saturday, March 24, 6 AM, or if strobilurin fungicide applied since Sunday, March 25, 6 AM.

This infection period accompanied by daytime rain to release ascospores.     Opportunity for surface fungicide kickback ends Friday, March 30, at 6 AM.         Opportunity for sterol inhibitor or strobilurin fungicide kickback ends Saturday, March 31, at 11 AM.         First generation lesions arising from this infection period would start appearing by Tuesday, April 17.          If conidia from 1st generation lesions spread infection, 2nd generation lesions could show as early as Monday, May 7.

Wetting period following  Saturday, March 31, 3 AM rain was too short for scab infection.      Approximately 0.20 inch rain and 25 leaf wet hours, with 38 F degrees average temperature during wet hours.        Cumulative scab ascospore release by end of this wetting period is roughly 5%.

Wetting period following  Sunday, April 01, 5 PM rain was too short for scab infection.      Approximately 0.18 inch rain and 18 leaf wet hours, with 41 F degrees average temperature during wet hours.        Cumulative scab ascospore release by end of this wetting period is roughly 5%.

******   Primary  Infection  Period  2  Details   ******     Begin: Thursday, April 12 at 11 AM    --->     Last rain hour: Sunday, April 15 at 4 AM.             Growth stage at start of period:  Between Tight Cluster and Open Cluster        This infection period accounts for roughly 2% of the year's total primary scab risk.               Approximately 0.12 inch rain and 26 leaf wet hours, with 44 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 15%.               Reliable pre-infection protection during this period expected if full dose + good coverage captan or EBDC fungicide applied since Saturday, April 7, 6 AM, or if strobilurin fungicide applied since Monday, April 9, 6 AM.

This infection period accompanied by daytime rain to release ascospores.          Opportunity for surface fungicide kickback ends Friday, April 13, at 7 PM.              Opportunity for sterol inhibitor or strobilurin fungicide kickback ends Sunday, April 15, at 11 AM.              First generation lesions arising from this infection period would start appearing by Friday, April 27.          If conidia from 1st generation lesions spread infection, 2nd generation lesions could show as early as Monday, May 14.

Wetting period following  Sunday, April 15, 2 AM rain was too short for scab infection.      Approximately 0.01 inch rain and 4 leaf wet hours, with 53 F degrees average temperature during wet hours.        Cumulative scab ascospore release by end of this wetting period is roughly 17%.

******   Primary  Infection  Period  3  Details   ******     Begin: Saturday, April 21 at 2 AM    --->     Last rain hour: Monday, April 23 at 6 PM.             Growth stage at start of period:  Between Full Bloom and Petal Fall        This infection period accounts for less than 1% of the year's total primary scab risk.               Approximately 0.01 inch rain and 59 leaf wet hours, with 52 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 17%.               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 Saturday, April 21, at 11 PM.   Counting from beginning of daytime ascospore release (low inoculum blocks), opportunity for surface fungicide kickback ends Sunday, April 22, at 4 AM.              Opportunity for sterol inhibitor or strobilurin kickback ends Tuesday, April 24, at 2 AM.   Counting from beginning of daytime ascospore release (low inoculum blocks), kickback window ends Tuesday, April 24, at 8 AM.              First generation lesions arising from this infection period would start appearing by Wednesday, May 9.          If conidia from 1st generation lesions spread infection, 2nd generation lesions could show as early as Monday, May 21.

******   Primary  Infection  Period  4  Details   ******     Begin: Sunday, April 22 at 11 AM    --->     Last rain hour: Monday, April 23 at 6 PM.             Growth stage at start of period:  Between Full Bloom and Petal Fall        This infection period accounts for roughly 72% of the year's total primary scab risk.               Approximately 2.80 inch rain and 41 leaf wet hours, with 51 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 80%.        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 3 PM.              Opportunity for sterol inhibitor or strobilurin fungicide kickback ends Wednesday, April 25, at 11 AM.              First generation lesions arising from this infection period would start appearing by Wednesday, May 9.          If conidia from 1st generation lesions spread infection, 2nd generation lesions could show as early as Monday, May 21.

Wetting period following  Friday, April 27, 2 AM rain was too short for scab infection.      Approximately 0.01 inch rain and 6 leaf wet hours, with 50 F degrees average temperature during wet hours.        Cumulative scab ascospore release by end of this wetting period is roughly 81%.

******   Primary  Infection  Period  5  Details   ******     Begin: Tuesday, May 1 at 2 AM    --->     Last rain hour: Saturday, May 5 at 7 AM.             Growth stage at start of period:  1 - 5 days after Petal Fall        This infection period accounts for roughly 15% of the year's total primary scab risk.               Approximately 0.65 inch rain and 115 leaf wet hours, with 51 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 93%.        Reliable pre-infection protection during this period expected if full dose + good coverage captan or EBDC fungicide applied since Friday, April 27, 6 AM, or if strobilurin fungicide applied since Sunday, April 29, 6 AM.

This infection period accompanied by daytime rain to release ascospores.          Opportunity for surface fungicide kickback ends Wednesday, May 2, at 1 PM.   Counting from beginning of daytime ascospore release (low inoculum blocks), opportunity for surface fungicide kickback ends Wednesday, May 2, at 5 PM.              Opportunity for sterol inhibitor or strobilurin kickback ends Friday, May 4, at 2 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 Tuesday, May 15.          If conidia from 1st generation lesions spread infection, 2nd generation lesions could show as early as Sunday, May 27.

******   Primary  Infection  Period  6  Details   ******     Begin: Thursday, May 3 at 2 AM    --->     Last rain hour: Tuesday, May 8 at 9 AM.             Growth stage at start of period:  6 or more days after Petal Fall        This infection period accounts for roughly 1% of the year's total primary scab risk.               Approximately 0.31 inch rain and 89 leaf wet hours, with 52 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 93%.               Reliable pre-infection protection during this period expected if full dose + good coverage captan or EBDC fungicide applied since Monday, April 30, 6 AM, or if strobilurin fungicide applied since Wednesday, May 2, 6 AM.

This infection period accompanied by daytime rain to release ascospores.          Opportunity for surface fungicide kickback ends Friday, May 4, at 8 AM.   Counting from beginning of daytime ascospore release (low inoculum blocks), opportunity for surface fungicide kickback ends Friday, May 4, at 12 PM.              Opportunity for sterol inhibitor or strobilurin kickback ends Sunday, May 6, at 2 AM.   Counting from beginning of daytime ascospore release (low inoculum blocks), kickback window ends Sunday, May 6, at 8 AM.              First generation lesions arising from this infection period would start appearing by Wednesday, May 16.          If conidia from 1st generation lesions spread infection, 2nd generation lesions could show as early as Thursday, May 31.

******   Primary  Infection  Period  7  Details   ******     Begin: Tuesday, May 8 at 2 AM    --->     Last rain hour: Thursday, May 10 at 11 AM.             Growth stage at start of period:  6 or more days after Petal Fall        This infection period accounts for less than 1% of the year's total primary scab risk.               Approximately 0.08 inch rain and 53 leaf wet hours, with 57 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 93%.        Reliable protection if strobilurin fungicide was applied since Friday, May 4, 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 Wednesday, May 9, at 12 AM.   Counting from beginning of daytime ascospore release (low inoculum blocks), opportunity for surface fungicide kickback ends Wednesday, May 9, at 5 AM.              Opportunity for sterol inhibitor or strobilurin kickback ends Friday, May 11, at 2 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 Sunday, May 20.          If conidia from 1st generation lesions spread infection, 2nd generation lesions could show as early as Thursday, May 31.

******   Primary  Infection  Period  8  Details   ******     Begin: Tuesday, May 8 at 6 PM    --->     Last rain hour: Thursday, May 10 at 11 AM.             Growth stage at start of period:  6 or more days after Petal Fall        This infection period accounts for roughly 8% of the year's total primary scab risk.               Approximately 1.93 inch rain and 43 leaf wet hours, with 58 F degrees average temperature during wet hours.          Cumulative scab ascospore release by end of this wetting period is roughly 99%.               Reliable protection if strobilurin fungicide was applied since Friday, May 4, 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 Wednesday, May 9, at 2 PM.              Opportunity for sterol inhibitor or strobilurin fungicide kickback ends Friday, May 11, at 6 PM.              First generation lesions arising from this infection period would start appearing by Sunday, May 20.          If conidia from 1st generation lesions spread infection, 2nd generation lesions could show as early as Thursday, May 31.