CITRUS SCAB : ITS CAUSE AXD CONTROL. 
17 
mediately became severe in this seed bed and increased rapidly in 
the nursery. 
During 1916, 1917, 1918, 1919, and 1920, the outbreaks of citrus 
scab in the bearing grapefruit orchards of Florida were in approxi- 
m— 
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 
/oo- 
^60 
\ 
\ Hi a A ffi / 
M/M/MUAf ;V 
40- 
IV 
(1 
d V 
8 '-£ 
/.<?- 
§ i\ 
1 1—± 
/S 3/ X5 i 
/92' ^/7csA#r 
-J3 ^_ 
/S 
i 
IS 
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 rather 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. 
4573°— 23— Bull. 1118 2 
