CITRUS scab: its cause and control. 



17 



mediately became severe in this seed bed and increased rapidly in 

 the nursery. 



Dm-ing 1916, 1917, 1918, 1919, and 1920, the outbreaks of citrus 

 scab in the bearing grapefruit orchards of Florida were in approxi- 



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Fig. 3.— Thermographic record of a typical week during the scab infection period, Orlando, Fla. 



mately average proportions, varying considerably from one locality 

 to another. These outbreaks were very sporadic and, with but few 

 exceptions, could not be anticipated. Often the disease did not 



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Fig. 4 —Precipitation and maximum and minimum temperatures at Orlando, Fla. , during January, 

 February, March, and April, 1921— a year of very little scab infection. 



develop in orchards with an abundance of scab on the old leaves, 

 but became#ather prevalent in properties hitherto apparently free 

 from scab. On the other hand, sour-orange and rough-lemon nursery 

 stock became severely affected during the spring of those years. 

 4.573°— 23— Bull. 1118- 2 



