340 The Philippine Journal of Science 1920 
of 1 to 200 or even 1 to 500 be attained in the driving rains and 
dripping dews of citrus-growing countries. Field experiments 
with neutral Bordeaux mixture entirely agree with this. It 
would seem logical from these tests to expect a lime solution, 
at a dilution of 1 to 500, to be the cheapest and most effective 
spray, in orchard practice, against citrus canker. 
In the absence of previous tests of the action of Bordeaux 
and Burgundy mixtures on bacterial plant pathogens, the fore- 
going tests are of interest and may be an index of the action 
of copper sprays against such other bacterial pathogens. It is 
unproved, however, since Pseudomonas citri may react to copper 
sprays differently from other bacterial plant pathogens. 
SUMMARY 
1. At exposures of 2\ minutes, phenol will kill Pseudomonas 
citri in a 3-day-old culture when used in a 1 to 100 solution; 
mercuric bichloride under the same conditions requires a 1 to 
20,000 solution; Liquor cresolis compositus requires a 1 to 300 
solution; formalin, a 1 to 20 solution. 
2. Of the commercially used spray mixtures, an emulsion of 
Liquor cresolis compositus and kerosene in 2\ minutes is entirely 
toxic to Pseudomonas citri at a dilution of 1 to 50 ; lime sulphur, 
32° Beaume, requires a 1 to 1,000 solution; copper sulphate, a 
1 to 200 solution ; neutral Bordeaux mixture has no bactericidal 
value whatsoever; Bordeaux 4-4-50 mixture is of doubtful bac- 
tericidal value even when undiluted; Bordeaux 4-6-50 mixture 
at 2^ minutes’ exposure is a safe bactericide even when diluted 
with 4 parts of water; lime when slaked is effective against 
Pseudomonas citri when diluted to a 1 to 1,000 solution. 
3. Burgundy 3-3-50 mixture and Burgundy 3-4-50 mixture 
have little or no bactericidal value against Pseudomonas citri 
even at the longer exposures. 
4. The use of formalin as a spray for the soil or the tree, or 
as a disinfectant, would seem to be uneconomical and in many 
cases entirely without value, except in a few remote instances 
where it might possibly be desirable partially to defoliate affected 
trees. 
5. The definite conclusion is put forward that copper precipi- 
tate sprays as bactericides against Pseudomonas citri are entirely 
valueless unless the lime is added in excess. The toxicity of such 
a spray then is of more or less value in proportion to the quantity 
