75 



REMEDIES FOR INSECTS AND DISEASE 



Fumigation 



Fumigation with hydrocyanic acid gas has become the main 

 reliance of the citrus fruit grower to preserve his trees from the 

 attacks of the various scale pests, and although the cost is higher, 

 probably twice that of spraying, the results are so much superior 

 and more lasting that in the end it is the cheaper method. These 

 superior results are due to several reasons : First, the gas, kept 

 about the tree for some time by the enclosing tent, completely 

 envelops and penetrates every part of it, while the spray, even 

 with the best kind of application, fails to touch all parts of the 

 tree owing to the thick foliage, which on the citrus trees is always 

 present. Even with defoliated trees it is difficult to reach every 

 part with spray, and it is seldom done in practice. We have yet 

 to find any insect attacking the citrus tree, except the red spiders 

 and similar mites, which are not as well, or better, reached by 

 the gas than by any spray which will not harm the tree, though 

 the thrips, owing to their flying abilities, are not well controlled 

 by fumigation, and the cheaper spray, more often repeated, has 

 secured the best results. Another point in favor of the gas treat- 

 ment is its better effect on the tree itself. 



All growers know that too frequent spraying will kill many of 

 the tender twigs and lower the vitality of the tree, as might be 

 expected to result from keeping a film of oily or soapy material 

 on the young growth, and especially on the leaves where are located 

 the breathing parts of the plant. One of the principal causes of 

 injury from the Black Scale, Mealy Bug, and White Fly is the 

 stopping of the leaf pores by the honey dew secreted by these 

 insects and the accompanying smut growth, and this condition is 

 not materially improved if, to destroy the scale, we apply another, 

 perhaps equally harmful coating, to the foliage. In comparison 

 with this checking of tree growth by the sprays, we have only 

 to note the considerable stimulation of growth usually shown by 

 the trees immediately after fumigation, to decide which benefits 

 the tree most, aside from the help derived from the more complete 

 destruction of the scale. 



