FUMIGATION OF CITRUS TREES. 61 



used, to make sufficient allowance for the irregularity in the surface 

 of the ground, which renders the possibility of leakage from under- 

 neath greater than in regular orchard work. 



DOSAGES IN GENERAL FUMIGATION. 



If the treatment is for any one of the insects mentioned previously, 

 the dosage recommended for that particular insect should be used. 

 Frequently, however, two, or even three, different species may be 

 found in the same grove. In such cases use that dosage which is 

 heavy enough to destroy the most resistant one. For instance, if 

 the purple and red scales, or the purple and black scales, occur in 

 the same orchard use dosage schedule No. 1 for an exposure of one 

 hour. If the red and black scales, or the yellow and black scales, 

 occur simultaneously, use a three-fourths schedule for one hour, 

 unless the black scale is in an advanced or matured stage, in which 

 case a full No. 1 schedule is required. 



TIME OF THE YEAR FOR FUMIGATION. 



Although fumigation is carried on in California at all times of the 

 year, there are certain periods in which the operations are more 

 general. There are two main factors to be taken into consideration 

 in fumigating, i. e., the species of scale insect and the condition of 

 the tree. As to the latter, it may be said that at certain periods of 

 the year the fruit is in such a tender condition that it can not with- 

 stand a heavy dosage without injury. This period is while the fruit 

 is of small size, usually from April until about August. The bulk of 

 fumigation in California at the present time is carried on between the 

 latter part of August and December. Probably the principal reason 

 for treating during this period is that the black scale is usually at 

 that time most successfully reached. Although the life history of 

 the black scale has never been thoroughly worked out for the region 

 in which these investigations were made, it is generally understood 

 that the majority of the insects of the largest and most regular brood 

 are hatched and in their least resistant stage during the months of 

 September and October. In some favorable seasons the eggs are 

 almost all hatched in August. 



The black scale occurs in practically every citrus-growing locality 

 in southern California, while the purple, red, and yellow scales are 

 more localized. Where any of these 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 dosage necessary to 

 destroy the most resistant species. The majority of these scale 

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

 purple scale alone, operations can be commenced as early in the 

 season as the trees are in a condition to withstand the heavy dosage 



