164 The Philippine Journal of Scrence 1921 
can be made on the economic feasibility of such control in one 
or two years. 
The fourth class would include the extremely susceptible 
grapefruit and lime varieties. Good control has been obtained 
on a few of these varieties, while on others the amounts of canker 
have at least been reduced. Such reductions however have been 
secured only after the application of an uneconomical number of 
sprays and much time in the careful pruning out of twig cankers. 
Under Philippine conditions, it is easily apparent that control 
methods on the American-grown grapefruit varieties and on the 
-West Indian lime varieties is not economically practical by the 
methods employed. With this class of citrus varieties therefore 
the results are similar to those obtained by Wolf. (21) 
TOTAL ERADICATION BY PRUNING AND SPRAYING 
The following experiment is presented to show the results 
obtained by another method of attack. An attempt was made 
on a small isolated citrus planting at Singalong, Manila, entirely 
to remove all leaf, twig, and branch cankers, thus eliminating 
all sources of reinfection, in the endeavor to determine whether 
or not eradication of citrus canker could be effected without 
the total destruction of trees. 
The planting consisted of two rows of nursery trees which had 
been allowed to mature in place, without removal to the orchard. 
-The lime trees were from four to five years old at the beginning 
of the experiment; some of the mandarin trees were three years 
old, while others of the same species, and the calamondin trees, 
were one year old. This planting was fairly well isolated from 
other sources of infection. The trees were cultivated, irrigated, 
and cared for entirely according to the usual American orchard 
practices. The treatment of this planting was as follows: 
August 19, 1917. Formalin 1-80 solution. 
September 1, 1917. Formalin 1-80 solution. 
September 10, 1917. Formalin 1-80 solution. 
September 16, 1917. Trees pruned for the removal of twig cankers. 
September 17, 1917. 4-450 Bordeaux mixture plus resin, sal-soda 
sticker. 
October 9, 1917. 4-4-50 Bordeaux mixture plus resin, sal-soda sticker. 
November 9, 1917. Neutral Bordeaux mixture plus powdered, neu- 
tral, lead arsenate to make 1-50 mixture. 
December 17, 1917. Neutral Bordeaux mixture plus cresol-kerosene 
emulsion. 
