CITRUS SCAB : ITS CAUSE AND CONTROL. 



27 



To determine whether or not Cladosporium citri Massee usually 

 found in older scab scars was responsible for the disease, a set of tests 

 parallel with those in Tables 6 and 7 was run. The organisms used 

 in this test were isolated from scab lesions from time to time, grown 

 and applied in a manner similar to that employed in the preceding 

 inoculation tests. The data from these tests, as indicated in Table 9 

 resulted from inoculations on fruit and leaves of the Satsuma orange 

 and grapefruit. 



Table 9. — Results of inoculations of Cladosporium citri on leaves and fruits of grapefruit 



and Satsuma orange. 



Part. 



Size (in 



six- 

 teenths 



of an 

 inch). 



Total 

 inocu- 

 lations. 



Dropped. 



Re- 

 main- 

 ing. 



Total 

 posi- 

 tive. 



Total 

 nega- 

 tive. 



Per- 



cent- 



posi- 

 tive. 



Degree of 

 infection. 



Grapefruit: 



Oct. 24, 1917.. 



Apr. 5, 1918... 



May 1, 1918. . . 



May 2, 1917... 



Apr. 10, 1918. . 



Apr. 22, 1920.. 



May 9, 1917... 



May 16, 1917.. 



Apr. 19, 1919.. 



May 8, 1920... 



Apr. 30, 1919.. 

 Satsuma orange: 



May 24, 1917.. 



June 17, 1920.. 



June 28, 1920.. 



Leaves 

 ..do.. 

 ..do.. 

 Fruit . 

 ..do.. 

 ..do.. 

 ..do.. 

 ..do.. 

 . -do. . 

 ..do.. 

 ..do.. 



-do., 

 .do., 

 .do.. 



0) 



(1) 



0) 



4 to 8 



6 to 8 



5 



8 to 16 



8 to 24 



12 



12 to 16 



16 to 20 



4 to 8 

 8 

 12 



24 



24 



22 



27 



28 



36 \ 



36 



38 



24 



41 



35 



32 

 27 

 32 







4 



9 



7.4 



7 



8.3 

 14, 

 13 



4 











9.3 

 11 

 



Slight. 

 Do. 

 Do. 

 Do. 

 Do. 

 Do. 

 Do. 

 Do. 



Do. 

 Do. 



1 Expanding. 



It is evident from Table 9 that the Cladosporium found in citrus- 

 scab lesions is not responsible for the disease. The checks in the 

 main show a slightly higher percentage of scab than do the inocula- 

 tions with Cladosporium organism but not higher than the checks 

 shown in Table 6 for the series of inoculations with the citrus-scab 



organism. 



SPRAYING EXPERIMENTS. 



Until recently very little spraying was done in Florida, even on 

 an experimental basis. Growers generally were not inclined to use 

 copper sprays, because such fungicides, while effective against scab, 

 also kill off the entomogenous fungi, resulting in a greatly increased 

 number of insect pests. Unless extra apphcations of insecticides 

 are made following applications of Bordeaux mixture, the damage 

 resulting from serious scale infection is hkely to more than offset the 

 benefits derived from scab control. On the other hand, growers who 

 used lime-sulphur solution claim this material is only partially effec- 

 tive against scab but even then is more desirable for citrus orchard 

 use than Bordeaux mixture. 



Similar results were obtained in experimental spraying by Steven- 

 son in Porto Rico (26, 26) and Grossenbacher (7), as well as by 

 Florida fruit growers who appUed the two materials for test purposes. 



