Table 2-1. Approximate wetting period required for primary apple scab infection at different air temperatures, and time required for development of conidia. (a)

Average temperature Average temperature Wetting period (hr)(b) Wetting period (hr)(b) Wetting period (hr)(b)  
Farenheit Celsius Light Infection Moderate Infection Heavy Infection Incubation period (days)(c)
78 25.6 13.0 17 26 -
77 25.0 11.0 14 21 -
76 24.4 9.5 12 19 -
63 - 75 172. - 23.9 9.0 12 18 9
62 16.7 9.0 12 19 10
61 16.1 9.0 13 20 10
60 15.6 9.5 13 20 10
59 15.0 10.0 13 21 12
58 14.4 10.0 14 21 12
57 13.9 10.0 14 22 13
56 13.3 11.0 15 22 13
55 12.8 11.0 16 24 14
54 12.2 11.5 16 24 14
53 11.7 12.0 17 25 15
52 11.1 12.0 18 26 15
51 10.6 13.0 18 27 16
50 10.0 14.0 19 29 16
49 9.4 14.5 20 30 17
48 8.9 15.0 20 30 17
46 8.3 15.0 23 35 -
45 7.8 16.0 24 37 -
44 7.2 17.0 26 40 -
43 6.7 19.0 28 43 -
42 6.1 21.0 30 47 -
41 5.6 23.0 33 50 -
40 5.0 26.0 37 53 -
39 4.4 29.0 41 56 -
38 3.9 33.0 45 60 -
37 3.3 37.0 50 64 -
36 2.8 41.0 55 68 -
33 - 36 0.6 - 2.2 48.0 72 96 -

a Adapted from Mills, 1944, as modified by A. L. Jones.

b The infection period is considered to start at the beginning of the rain.

c Approximate number of days required for conidial development after the start of the infection period.