Figure 14.  Wetting period (in hours) required for apple scab infection at different air temperatures, and time required for development of conidia by lesions at different air temperatures. W.D. Mills, Cornell University, as modified by A.L. Jones, Michigan State University.

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Wetting period (HOURS) Average Temperature (F) Average Temperature (C) Light Infection Moderate Infection Heavy Infection Incubation Period (days) 78 25.6 13 17 26 ... 77 25.0 11 14 21 ... 76 24.4 9.5 12 19 ... 63-75 17.2-23.9 9 12 18 9 62 16.7 9 12 19 10 61 16.1 9 13 20 10 60 15.6 9.5 13 20 11 59 15.0 10 13 21 12 58 14.4 10 14 21 12 57 13.9 10 14 22 13 56 13.3 11 15 22 13 55 12.8 11 16 24 14 54 12.2 11.5 16 24 14 53 11.7 12 17 25 15 52 11.1 12 18 26 15 51 10.6 13 18 27 16 50 10.0 14 19 29 16 49 9.4 14.5 20 30 17 48 8.9 15 20 30 17 47 8.3 17 23 35 17 46 7.8 19 25 38 17 45 7.2 20 27 41 17 44 6.6 22 30 45 17 43 6.1 25 34 51 17 42 5.5 30 40 60 17