TIME OF YEAR FOR FUMIGATION. 49 



of the insects of the large and more regular ])rood are hatched and 

 m their least resistant stage during September and October. In 

 some favorable seasons the eggs are almost all hatched in August. 

 Moderately light fumigation dosage may be used against the black 

 scale during this period with success. 



The black scale occurs in practically every citrus-growing locality 

 of southern California, while the purple, red, and yellow scales, the 

 other principal citrus pests, are more localized. A heavier dosage 

 is used for the latter insects than for the black scale. Where the 

 other species occur in orchards infested with the black scale, it is 

 a common practice to fumigate during the regular black-scale 

 period, using the heavier dosage. The majority of these scale insects 

 can thus be caught at one time. When fumigating for the purple 

 scale alone, operations may be commenced as early in the season as 

 the trees are in a condition to withstand the heavy dosage without 

 injury, although probably it would be preferable to fumigate a little 

 later in the fall. The purple scale is to be found in the egg stage 

 throughout the year. There is a period in the fall and one in the 

 early spring, however, during which the smallest proportion of eggs 

 is to be found. With dosages lower than those of eradication, the 

 best work can be accomplished at these times. 



The red and yellow scales are viviparous and can be successfully 

 destroyed throughout the year. 



In fumigating for any of the scale-insects there is one point 

 worthy of consideration. Aside from trying to save the tree from 

 destruction or from having its vitality'" impaired by the attack of 

 scale pests, the orchardist fumigates principally in order to have 

 his fruit come into the packing house as clean as possible. It would 

 be well, therefore, to fumigate as nearly as possible to the time 

 which would insure him the cleanest fruit. Although lemons are 

 gathered throughout the entire year, the bulk of the orange crop is 

 taken during the first six months. Thus fumigation during the fall 

 and early winter would be sure to place the cleanest fruit in the 

 packing house. If carried on in the late spring or earl}^ summer, 

 such insects as remain undestroyed would have the opportunity to 

 breed through a period of several months and infest much fi-uit. 



FUMIGATION DURING THE BLOSSOMING PERIOD. 



The statements by experts on fumigation as to the amount of 

 injury resulting from work while the trees are m blossom are ver}?" 

 conflicting. Some fumigators hold that a ver}^ light dosage will 

 destroy the tender blossoms, while others believe that the blossoms 

 will stand a heavy dosage. In order to decide this point much experi- 

 mentation was carried on and many observations made throughout 

 7748&— Bui. 79—09 1 



