THE CAMPHOR SCALE 15 



The proportion of camphor scales killed by a given quantity of 

 oil depends largely on the intensity of the infestation. The scales 

 are most easily killed on the lightly infested plants. In one spray 

 test in which the branches were marked off in units 1 cm long 

 and these units were classified according to the percentage of twig 

 area covered by scales, the units having less than 10 percent of the 

 twig area covered by scales showed a mortality of approximately 

 90 percent, whereas on those having 90 percent or more of the sur- 

 face covered less than 15 percent of the scales were killed. Because 

 of the effect of excessive quantities of oil on the plant, it is impossible 

 to use enough oil to secure control in one application when plants 

 are heavily infested. In such cases additional sprays must be ap- 

 plied during the growing season, but oil sprays for fig trees should 

 be confined to dormant applications. 



In selecting the time to apply spring or summer sprays, it should 

 be kept in mind that the younger the scales the more susceptible 

 they are to oils. Practically all the exposed scales of the first and 

 second instars, and those of the third instar that are not more than 

 1 week past the second molt, can be killed with sprays containing 

 1 percent of oil. As the time of appearance of these stages de- 

 pends on the temperature, no definite dates for best results can be 

 given, but the most favorable time for application can be determined 

 from the time of emergence of the young of each brood, which can 

 be fairly easily observed. The newly settled scales are white, about 

 the size of a pinhead, and conspicuous on the plant (fig. 3). The 

 range of dates within which their appearance may be expected is 

 given on page 10. Those who wish to get the maximum benefit from 

 summer sprays should keep the infested plants under observation 

 and determine the date of appearance of the new brood. Summer 

 temperatures in New Orleans are usually so uniform that sprays 

 can be properly applied at a constant time after the emergence 

 of the first instar of each brood. In 1926, 1927, and 1928, the best 

 time for summer sprays was found to be at the intervals shown in 

 table 1 after the first appearance of the young of the first and second 

 broods. 



Table 1. — Period from the emergence of the first instar of the camphor scale 

 to the best time for summer-spray applications, 19.26, 1927, and 1928 



Brood 



Period after emergence 



1926 



1927 1928 



First - - - 



Days 

 56 

 38 



Days 

 58 

 38 



Days 



58 





35 







At the times shown in table 1 not more than 3 to 5 percent of the 

 scales were reproducing, and nearly all the others were in stages 

 capable of being killed by summer sprays. Tests have proved that 

 the oil remaining after plants have been sprayed with 1 percent of 

 oil is sufficient to destroy most of the crawlers emerging for a period 

 of 2 weeks after application. Consequently, when sprays are ap- 



