CITRUS scab: its cause and control. 



19 



Table 4. — 3fean temperature and precipitation at Orlando, Fla., during the months of 

 May, June, July, and August in the years 1918, 1919, and 1920. 



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







May. 



June. 





Temperature. 



Precipitation. 



Temperature. 



Precipitation. 



Year. 



Extremes. 



Mean. 



De- 

 par- 

 ture 

 from 

 nor- 

 mal. 



Total. 



De- 

 par- 

 ture 

 from 

 nor- 

 mal. 



Extremes. 



Mean. 



De- 

 par- 

 tine 

 from 

 nor- 

 mal. 



Total. 



De- 

 par- 





Maxi- 

 mimi. 



Mini- 

 mum. 



Maxi- 

 mum. 



Mini- 

 mum. 



ture 

 from 

 nor- 

 mal. 



1918 



87.9 

 89.3 

 84.3 



63.1 

 63.2 

 60.8 



75.5 

 76.2 

 72.6 



-1.4 



-.7 



+1.6 



2.11 

 10.37 

 6.72 



-1.7 

 +6.56 

 +4.70 



93. 2 68. 8 

 90.5 68.3 

 91. 2 67. 8 



81.0 

 79.4 

 79.5 



+0.6 



-1.0 



-.9 



5.37 

 5.19 

 5.89 



1.89 



1919 



1920 



-2.07 

 — 1.27 









July. 



August. 



For 4 months. 



Year. 



Temperature. 



Precipita- 

 tion. 



Temperature. 



Precipita- 

 tion. 



De 



fro 



Darture 

 m nor- 

 mal. 



Mean 

 tem- 

 pera- 

 ture. 





Extremes. 





De- 

 par- 

 ture 

 from 

 nor- 

 mal. 



Total. 



De- 

 par- 

 ture 

 from 

 nor- 

 mal. 



Extremes. 



Mean. 



De- 

 par- 

 ture 

 from 

 nor- 

 mal. 



Total. 



De- 

 par- 

 ture 

 from 

 nor- 

 mal. 





Pre- 

 cipi- 

 ta- 

 tion. 





Maxi- 

 mum. 



Mini- 

 mum. 



Mean. 



Maxi- 

 mum 



Mini- 

 mum. 



pera- 

 ture. 



1918.... 



1919 



1920.... 



90.8 

 92.4 

 92.7 



69.4 

 70.3 

 70.4 



80.1 

 81.4 

 81.6 



-0.2 



-.7 

 -.5 



12.3 

 11.49 

 7.49 



+ 5.5 

 +4.24 

 +.24 



94.1 

 94.3 

 93.3 



70.2 

 70.5 

 69.6 



82.2 

 82.4 

 81.4 



+0.1 

 +.3 



-.7 



3.34 

 5.49 

 5.35 



-3.81 

 -1.69 

 +1.8 



-0.9 



-2.1 

 -.5 



-1.9 

 +6.04 

 +5.37 



79.7 

 79.8 

 78.77 



It will be noted that in spite of the fact that the mean tempera- 

 ture is in general well above the limits set by Fawcett, the mean 

 minimum temperatures for summer are usually well within that 

 range, but it is probable the temperature does not remain in that 

 lower zone sufficiently long for infection to progress at a rapid rate. 



If it is assumed that the pathogen is present in quantity, there 

 are thi'ee other factors which play their parts in completing infec- 

 tion, viz, (1) suitable temperature limits, (2) abundant moisture, 

 and (3) host parts in a stage of development susceptible to infection. 

 The relative scarcity of citrus scab in both orchards and nurseries 

 situated in the drier sections of Florida and in the drier seasons, 

 together with the fact that citrus scab has not been able to estab- 

 lish itself in California lemon orchards with their drier climatic 

 conditions, is strong evidence that this fungus is largely dependent 

 upon certam weather conditions to cause infection, namely, abun- 

 dant moisture during the period when leaves are expanding and 

 fruit is setting. Such weather seldom occurs in the relatively dry 

 citrus . regions of California at times when the plant is susceptible 

 to infection; hence, the absence of scab and its resulting financial 



