CITRUS MELANOSE AND ITS CONTBOL 
27 
Table 4. — Combined results of nielanose inoculations on citrus fruits at Or- 
lando, Fla., 1919 to 192k 
Num- 
ber of 
varie- 
ties in 
the 
test 
Diameter 
in six- 
teenths of 
an inch 
Inoculations 
Degree of infection 
"Water blank 
checks 
Num- 
ber 
Per- 
cent- 
age 
posi- 
tive 
Kind of citrus 
Num- 
ber 
Per- 
cent- 
age 
posi- 
tive 
7 
7 
2 
2 
2 
2 
1 
1 
4 
fO'to'4 
5 to 8 
9 to 12 
13 to 16— 
17 to 20— . 
21 to 24-.. 
25 to 28— 
29 to 32— 
f0to4 
5 to 8 
9 to 16 
17 to 24.... 
25 to 32— . 
33 to 40— 
Ulto48— . 
8 
40 
275 
202 
216 
194 
328 
190 
76 
130 
20 
277 
301 
267 
288 
226 
56 
28 
32 
36 
30 
20 
125 
92 
49 
56 
55 
37 
36 


74 
75 
47 
76 
76 
35 

100 
100 
100 
100 
100 
100 
100 
do 
Medium.. 
Orange 
do 
Slight to very slight .. 
Very slight 
40 

Very severe to severe. . 
Severe 
150 

Medium 
143 
40 

Grapefruit 
do 
do 
Slight 

82 
10 
20 
20 
2 

TTirrnqnat 

20 to 24-.. 
10 to 18— . 
8 to 10 
8 to 10 
10 
Slight to very slight... 

Lime- 
Sour orange. .. .. 
Bergamot orange. . . .. 
do 
do 
:::::::::::::::: 
Oalamondin 
i 
Citrus hybrids 
10 to 12— 
Very severe to medium 
33 
From the inoculation tests reported in this bulletin, together with 
many careful observations in groves and experimentally sprayed 
plots, it is evident that the young fruit of the orange is at first very 
susceptible to infection. It becomes resistant gradually and de- 
velops immunity when it has reached about 1% inches (38 milli- 
meters) in diameter. The grapefruit starts life considerably more 
susceptible to infection than the orange, and it, too, becomes pro- 
gressively resistant as it increases in size, reaching immunity when 
the fruit is about 2y 2 inches (63 millimeters) in diameter. 
The calendar date at which spring-bloom fruit reaches these stages 
of growth varies considerably, not only from year to year but also on 
the same tree during any given season, because of the lengthy blos- 
soming period extending from February through the greater part 
of March. However, the majority of the fruit from the spring 
bloom in the neighborhood of Orlando, Fla., seldom reaches this 
immune stage of growth before May 20 and rarely later than 
June 10. 
MISCELLANEOUS INOCULATIONS 
In addition to the foregoing inoculation experiments, tests were 
made to determine whether' or not the mycelium of Phomopsis citri 
could cause infection, and other tests were made with spore suspen- 
sion of this fungus to determine the effect of spray coatings, boiling 
of the inoculum, and aging of the inoculum upon subsequent infec- 
tion. These tests were repeated several times and may be summar- 
ized as follows : Fully 200 inoculations were made with the mycelium 
of P. citri on tender orange and grapefruit leaves. In practically 
every case infection failed to develop, but on a few of the inoculated 
leaves occasional melanoselike spots appeared. If these spots were 
