10 
BULLETIN 1118, U. S. DEPARTMENT OF AGRICULTURE. 
grapefruit are likely to be misleading. Rough-lemon and sour- 
orange nursery trees arc exceedingly susceptible to scab infection 
and are equally affected if not more severely attacked during the 
hot rainy summer season than is the case in the spring. That this 
condition exists is corroborated by letters on file in the Office of Fruit- 
Disease Investigations from five of the larger commercial nurseries 
in Florida. 
The United States Department of Agriculture maintains a nursery 
of rough-lemon, sour-orange, and grapefruit seedlings at Orlando, 
Fla., for experimental purposes. This nursery was set out in March, 
1918. The flushes which developed during April and May of that year 
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Fig. 2.— Precipitation and maximum and minimum temperatures at Orlando, Fla., during January, 
February. March, and April, 1915— a year of severe scab infection. 
were affected by citrus scab, but not nearly so severely as was the 
case during the rainy summer weather. The flush which developed 
late in the fall was comparatively free from citrus scab, in spite of 
foci of infection on the older leaves. Similar conditions were noted 
in this nursery during the years of 1919 and 1920, viz, scab attacks 
the nursery stock more severely during the rainy season in summer 
than is the case during the spring or fall. As stated in another place, 
the spring of 1921 was quite dry. Little or no citrus scab developed 
in this nursery during that period. The same applies to a new seed 
bed of similar seedlings. As soon as the rains set in citrus scab im- 
