DEGREE OF INFECTION OBTAINABLE. 59 



mixturos of spores for about 2 cents a tree. At this price there is, of 

 course, a fair iuar<2;in of jjrofit. The aulliors, with kua])sa('k sj)rayers, 

 and with the assistance of hiborers at $1.50 j)er (hiy, have been able 

 to spray 3 trees for 1 cent. One pjrower, by using a barrel outfit, 

 with tlie aid of a boy at the jMinip, sprayed 100 trees witli 50 <j^allons 

 of sohition in one hour. If one has to ])urcliase fun<^us-infected 

 leaves the cost is correspondingly higher. The very low cost of 

 spraying fungous solutions can not fairly be compared with that of 

 spraying insecticitles or of fumigation if one considers the results 

 obtained. Certain expenditures for either of these last methods of 

 control may be expected to ])roduce defmito results that can be figured 

 in dollars and cents if the remedy is properly applied. The returns 

 for money spent in spraying fungus are never assured; if there is no 

 infection in the grove at the time of the first application, the spraying 

 may result in a temporary fungous control within three years, or it 

 may ultimately cost the grower, through failure of the fungi to spread 

 properly, much of his foliage and bearing wood as a result of secondary 

 scale attack, to say nothing of a sharp falling off in the bearing of his 

 trees, and other losses incident to white-fly infestation. 



DEGREE OF INFECTION OBTAINABLE. 



In field experiments it is impossible to distinguish the extent of 

 direct infections with certainty, smce natural spread usually takes place 

 before the entire direct infection manifests itself. Even under the 

 most favorable climatic conditions for fungous spread, only a very 

 small percentage of the immature white flies which are exjjosed to 

 spores from freshly matured pustules of red and yellow Aschersonias 

 becomes infected. Many field tests have been made on a small 

 scale, in which one or more branches heavily infested with white-fly 

 larvae and pupiB have been dipped or drench-sprayed with concen- 

 trated mixtures of Aschersonia spores.^ In no instance has the 

 resulting infection amounted to more than 5 per cent of the number 

 of insects alive at the time of the introduction, and the apparently 

 (Urect infection has rarely exceeded 1 per cent. In ordinary spraying 

 on a large scale the direct infection on the parts of the tree reached 

 by the spray is usually but a very small part of 1 per cent. 



The brown fungus has proved much more difficult of spread arti- 

 fically, as regards the degree of infection which it is possible to obtain 

 by the methods tested as described elsewhere. During September 

 and October, the most favorable season for brown fungus, introduc- 

 tion and infection are rarely secured on more than 1 per cent of white- 

 lly-infected leaves ^ which have been dipped in water mixturos of 



1 Tests with red Aschersonia for the citrus white fly and with the yellow .Vschcrsonia for the cloudy- 

 winf;cd white fly are particularly referred to. 



' Since the brown fungus generally destroys all of the white flics on a leaf upon which it becomes estab- 

 lished, it appears to the authors that the number of leaves infected is a better standard than is the actual 

 number of insects infested. 



