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Weather data for South Burlington VT. Forecast values begin May 18, 2013

Key Apple Scab Dates

First primary scab infection period (including those with only night rain) starts:
May 11, Saturday 1AM

First primary scab infection (including those with only night rain) that lasts
past Half Inch Green starts: May 11, Saturday 1AM

#DIV/0!

Date of 'Final' significant primary scab ascospore release is:
April 18, Thursday

    '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

#N/A

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.

#DIV/0!

#N/A

#DIV/0!

     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.