CITRUS scab: its CAUSE AND CONTROL. 



15 



Table 3. — Mean temperature and precipitation at Orlando, Fla., during the niontJis 

 of January, February, March, and April in the years 1914, 1915, and 1921. 



[Temperature data are statedln degrees F., precipitation data in inches.] 









January. 



February. 



Year. 



Temperature. 



Precipitation. 



Temperature. 



Precipitation. 





Mean. 



Depar- 



tin-e 



from 



normal. 



Total. 



Depar- 

 ture 

 from 



normal. 



Mean. 



Depar- 

 ture 

 from 



normal. 



Total. 



Depar- 

 ture 

 from 



normal. 



1914 



69.4 

 58.7 

 63.7 



+0.2 

 - .5 

 +3.5 



5.23 



4.36 



.52 



+2.83 

 +1.96 

 -2.08 



62.2 

 60.3 

 64.1 



+1.0 

 - .9 

 +2.6 



3.31 

 4.34 

 1.76 



+0.62 



1915 



+1.65 



1921 



- .89 









March. 



April. 



Total depar- 

 ture from 

 normal. 



Year 



Temperature. 



Precipitation. 



Temperature. 



Precipitation. 





Mean. 



Depar- 

 ture 

 from 



normal. 



Total. 



Depar- 

 ture 

 from 



normal. 



Mean. 



Depar- 

 ture 

 from 



normal. 



Total. 



Depar- 

 ture 

 from 



normal. 



Tem- 

 per- 

 ature. 



Pre- 

 cipita- 

 tion. 



1914 



62 



59.2 



73.2 



-5.6 



-8.4 

 +5.8 



2.10 

 1.41 



.87 



-0.20 

 - .89 

 -1.44 



72.9 

 68.4 

 72.6 



+2.1 

 -2.4 

 + 1.5 



2.25 

 .10 

 1.51 



+ .29 

 -1.10 



- .82 



- 2.3 

 -12.2 

 +13.4 



+3.54 



1915 



+1.62 



1921 



-5.23 







It will be noted that the mean temperatures for all three seasons 

 are reasonably well within the infection range mentioned by Fawcett, 

 while the rainfall was above normal during 1914 and 1915, years of 

 citrus-scab abundance, and considerably below normal for the same 

 period in 1921, when citrus scab was very slight. Figure 2 shows the 

 daily range of temperature and the precipitation during these four 

 months of 1915, while Figure 3 is a thermographic record '^ for a 

 representative week during the scab season. Figure 4 gives the 

 temperature range during the comparatively scab-free spring of 

 1921. With the progress of the rainy season of the summer of 1921 

 numerous complaints were registered in regard to a severe citrus- 

 scab outbreak on the current crop of June bloom fruit, especially on 

 trees which showed little or no spring infection but abundantly 

 supplied with affected leaves from the 1920 growth. Many nurseries 

 which were only slightly affected with scab during the spring of 1921 

 were very severely attacked during the summer of that year. It 

 thus appears that infection is possible over a wide range of tempera- 

 tures, and that moisture conditions during periods when young 

 flushes are putting out determine in the main the seasonal prevalence 

 of citrus scab. 



Conclusions regarding the general behavior of the disease on its 

 several hosts when based on the behavior of the disease on bearing 



* The graphs shown in Figures 3 and 6, while not dependable for maximum and minimum range, give a 

 rather accurate account of the length of time that the high and low temperatures were maintained. 



