16 Diseases of Economic Plants 



tective sprays are usually given at intervals of from ten to 

 fourteen days, though special rules must govern special cases. 



The chief protective applications are : — 



Bordeaux mixtui-e, full strength or weak. 



Ammoniacal copper carbonate. 



The latter solution possesses the advantage that it does 

 not spot the fruit and may therefore be used near the period 

 of maturity, when the Bordeaux mixture, owing to its 

 spotting effect, would be less desirable. 



Lime-sulfur mixtures. 



Sulfin- and lead arsenate. 



5. Excision of the affected parts. — Examples: Ash 

 white-rot. Excision is resorted to chiefly in the case of trees 

 which from their location or quality possess value suffi- 

 cient to warrant the necessary outlay of labor. It is so 

 practiced as to remove the diseased wood and sufficient of 

 the healthy wood to expose an entirely uncontaminated sur- 

 face. The wounded surface is then treated with an antiseptic 

 such as tar or carbolineum. 



6. Removal and destruction of diseased twigs, leaves, 

 or fruit. — Examples: fire-blight, peach brown-rot. The 

 removal and destruction of diseased parts diminishes the 

 number of bacteria, spores, etc., that are available to spread 

 the disease and thus lessens infection. Mummified fruit 

 should be picked from the plant or the ground and destroyed, 

 or it may be removed by appropriate pasturage by fowls, 

 swine, etc. Affected leaves in many instances should be 

 similarly removed. Blighted twigs and cankers should be 

 cut out when seen. 



7. Removal, in whole or in part, of complementary hosts. 

 — Examples: apple rust, wheat rust. Complementary hosts 

 always serve as multiplying places for the causal parasite, 

 and in some instances are absolutely essential to its hiberna- 

 tion. Such complementary hosts should, when practicable, 

 be removed from the immediate vicinity, and, when possible, 

 not allowed to exist within considerable distance, one eighth 



