2018 Crop Protection Guide for Tree Fruits in Washington

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Saturday, July 21, 2018

Mills' Apple Scab Infection Table

Approximate Wetting Period Required for Primary Apple Scab Infection at Different Air Temperatures and Time Required for Development of Conidia
  Degree of Infection  
Average temperature (°F) Light (hours) Moderate (hours) Heavy (hours) Lesion Appearance (days)
33–36 48 72 96 ?
38 37 50 64 ?
39 33 45 60 ?
41 26 37 53 ?
42 23 33 50 17
43 21 30 47 17
44 19 28 43 17
45 17 26 40 17
47 15 23 35 17
48 15 20 30 17
49 14.5 20 30 17
50 14 19 29 16
51 13 18 27 16
53 12 17 25 15
58 10 14 21 12
59 10 13 21 12
60 9.5 13 20 11
63–75 9 12 18 9
78 13 17 26  
Hours of wetness from the beginning of rain (data of W.D. Mills as modified by A.L. Jones). If sporulating lesions are already present, wetting periods required to produce secondary infections are approximately 3 hours less than those listed in the table for primary infection. Number of days required for lesions to appear after infection has been initiated. No further wetting is required. Additional days may be required if conditions are unfavorable for lesion development (prolonged periods above 80 °F or very dry weather).

 

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