DEGKEE OF INFECTION OBTAINABLE. 59 
mixtures of spores for about 2 cents a tree. At this price there is, of 
course, a fair margin of profit. The authors, with knapsack sprayers, 
and with the assistance of laborers at $1.50 per day, have been able 
to spray 3 trees for 1 cent. One grower, by using a barrel outfit, 
with the aid of a boy at the pump, sprayed 100 trees with 50 gallons 
of solution in one hour. If one has to purchase fungus-infected 
leaves the cost is correspondingly higher. The very low cost of 
spraying fungous solutions can not fairly be compared with that of 
spraying insecticides or of fumigation if one considers the results 
obtained. Certain expenditures for either of these last methods of 
control may be expected to produce definite 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, since 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 exposed 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 
larvse and pupse have been dipped or drench-sprayed with concen- 
trated mixtures of Aschersonia spores. 1 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 
direct 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- 
fly-infected leaves 2 which have been dipped in water mixtures of 
1 Tests with red Aschersonia for the citrus white fly and with the .yellow Aschersonia for the cloudy- 
winged white fly are particularly referred to. 
3 Since the brown fungus generally destroys all of the white flies 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. 
