ENTOMOLOGY ' 



387 



The proportions here recommended are thoroughly effective 

 for the black scale at the proper season, and measurably effective also 

 for the California red scale and the purple scale. Where the treat- 

 ment is designed to be one of extermination for these latter scale 

 pests, from one-third to one-half more of cyanide and acid is em- 

 ployed, as indicated by the subjoined table, furnished by Mr. G. 

 Havens, of Riverside. The amounts here recommended may be 

 employed also for compact trees with dense foliage or in moist coast 

 regions where stronger doses are needed. 



Excessive Amounts of Chemicals Used for A bsolute Extermination of 



Scale Insects. 



The duration of the treatment indicated in the second table 

 varies with the size of the tree, but in general at least forty minutes 

 should be allowed. 



In Florida fumigation for the white fly can be successfully 

 practiced only during the short period in winter when the insect 

 does not occur in the winged stage. This period covers from two 

 and a half to three months, namely, December, January, and Feb- 

 ruary, varying with the climatic conditions of different years. This 

 is the dry season for Florida, and the trees are in a dormant condi- 

 tion, with the leafage well matured and hardened, and it is possible 

 to apply a greater strength than would be safe under California 

 conditions. The strength recommended is approximately the same 

 as for deciduous nursery stock, viz., 1 ounce of cyanide to 100/115 

 cubic feet of space, with a duration of 40 minutes. 



General Directions. In the fumigation of growing stock, citrus 

 or other, the treatment consists in inclosing the tree with a tent and 

 filling the latter with poisonous fumes generated in the same way 

 as described for nursery stock except that less of the chemicals is 

 used. The treatment is made at night for trees in foliage, which 

 includes all work in citrus orchards, to avoid the much greater 

 likelihood of injury to tender foliage in the sunlight. The vessels 

 for setting off the charges of cyanide and acid may be, for small 

 doses, any ordinary earthenware jars. For large tree;? requiring 

 heavy doses, tall wooden pails have proved more satisfactory, two 

 generators being employed for the very largest trees. 



