-2- 



Table 1. Hours of vretting needed at different temperatures f'ir apple Scab primary 

 infection en 'onsp rayed leaves early in the season.* 



Temperatures (op.) Light Infection Moderate Infection Heavy IrXaction 



— - r— — 



h^, 20 26 iiO 



50 li4 19 29 



55 12 16 2U 



60 10 13 20 



65-75 9 12 18 



78 12 17 26 



Incubation Period: Incubation period covers the time from penetration and 

 establishment of infection to the appearance of the disease lesions. It too varies 

 in length i*d.th the temperature, and also v/ith the kind of disease. The lower the 

 daily temperatures after infection takes place, the longer vdll be the incubation 

 period. Y/. D. Llills in IJev; York State found that the mean temperat,ure for the 

 first 5 days after infection vras a more reliable criterion than the mean temperature 

 of the entire incubation period in arriving at an accurate relationship betvreen 

 temperature and length of incubation period. The data in Table 2 show the relation- 

 ship between the mean daily temperature for the entire incubation period and the 

 length of that period, as compared Tdth the mean temperature for the first 5 days. 

 One value of these data lies in the ability of one to figure back after scab spots 

 appear and determine through temperature records which vret period caused the 

 infection. Also, it is possible to note the mean daily temperatures for five days 

 after an infection period and then figure out when the spots will show up. This 

 latter advantage is by far the mere useful one to the grower. 



Table 2 . Observations on incubation periods for Apple Scab in 'western Nev/ York, 

 based upon the first important infection period of each year for 27 years. -;;- 



i.'iean temperature (*^F.) for Approximate number of Mean temperature (°F.) of 

 the entire incubation days in the incubation first five days after 

 period period infection 



— 19 35-37 



18 38-l;0 



U8-U9 17 Ul-ii3 



50-51 16 UU-U6 



52-53 15 U7-h9 



5U-55 11 50-53 



56-57 13 Sh-S6 



58-59 12 57-59 



60 11 60-62 



61-62 10 63-65 



63-6ii 9 66-68 



65-66 8 69-72 



7 73- 7U 



* Data from reports by '-H. D. Mills, Cornell University 



