Weather data for Hollis NH. Forecast values begin September 12, 2012

Key Apple Scab Dates

First primary scab infection period (including those with only night rain) starts:
April 1, Sunday 5PM

First primary scab infection (including those with only night rain) that lasts
past Half Inch Green starts: April 1, Sunday 5PM

If present, lesions from the season's first primary scab infection period
would become visible and begin producing conidia for spread of secondary scab on:
May 8, Tuesday

Date of 'Final' significant primary scab ascospore release is:
May 22, Tuesday

    'Final' defined as best guess of 99+% cumulative ascospore release, and high probability that at least 95% of ascospores have been released.
     Secondary scab protection and scouting should continue until 2nd generation lesions from the season's final ascospore release have had time to begin appearing.
     See 'Scab Lesion Appearance Dates' chart, 'Postbloom Secondary Scab Protection' table, and the estimated lesion appearance dates below.

Scab lesion appearance dates chart

Postbloom secondary scab protection spray dates

About 50% or more of primary scab potential has had time to start appearing
as 1st generation foliar lesions by:
May 20, Sunday

This is a good date to begin intentional scab scouting.
Finding scab infections on fewer than 6 leaves per 100 clusters/shoots indicates that early-season primary scab control was successful. But continued sampling until 2nd generation lesions from the season's final primary scab infection period have had time to begin appearing is recommended before relaxing protection against secondary scab. This is because: 1) light infestation of 1st generation lesions can be difficult to detect, 2) lesions from later primary scab infection periods have not yet had time to begin appearing, and 3) infections delayed but not killed by fungicide application or by partial resistance of older leaves may begin to show after the estimated appearance dates.

1st generation lesions from the FINAL significant primary scab
ascospore release have had time to begin appearing by:
June 3, Sunday

About 50% or more of primary scab potential has had time to begin appearing
as 2nd generation foliar and fruit lesions by:
June 1, Friday

2nd generation lesions from the FINAL significant primary scab
ascospore release have had time to begin appearing by:
June 14, Thursday

     Accurate evaluation of scab control requires weekly inspection of 100+ shoots of susceptible cultivars for scab lesions until this date has passed.
     Finding 6 or more leaves with fresh scab lesions per 100 clusters/shoots before terminal bud set in a commercial orchard suggests that fungicide selection and spray intervals need to be adjusted to suppress spore production, and to protect fruit and foliage from new infections for at least 4 weeks until active scab lesions exhaust their supply of spores.
     Finding active scab lesions indicates need to identify the cause in order to prevent reoccurence. Common causes are inadequate fungicide coverage, timing, or dosage.