56 MANUAL OF FRUIT DISEASES 



gas from coal. It should not be called gas-tar, which is a 

 term more loosely used. Some growers have complained of 

 injury to trees from the use of coal-tar, but in such cases the 

 material has usually proved to be something other than coal-tar. 



The effectiveness of spraying for canker is a question fre- 

 quently raised. As a preventive this operation is worthy of 

 attention ; as a cure it is out of the question, for once the fungus 

 is in the bark the spray material cannot reach it. 



If an orchardist desires to grow susceptible varieties, the 

 canker menace may be obviated to a considerable extent by 

 working over the larger limbs of more resistant varieties to the 

 one desired. This has been done with apparent success in a 

 few instances. The difficulties involved are that pruning must 

 be done every year in order to remove all sprouts from the 

 stocks, and that the renewal of old branches cannot be effected 

 so rapidly. Such treatment also throws the bearing area higher 

 in the air; so that in the case of erect-growing varieties such 

 as the Twenty Ounce, it makes pruning, spraying and picking 

 more difficult. 



For the control of black-rot of apples, bordeaux mixture is 

 said to be more effective than lime-sulfur. Apply bordeaux 

 4^-50 as follows : (1) about July 15, when the disease is just 

 appearing, and (2) two weeks later. As a matter of precaution 

 against damage in storage, avoid injuring the fruit in any way. 

 Spraying for leaf -spot should be done according to the schedule 

 outlined for apple-scab (see page 12). 



REFERENCES 



Hesler, L. R. Black rot, leaf spot, and canker of pomaceous fruits. 



Cornell Univ. Agr. Exp. Sta. Bui. 379 : 51-148. 1916. 

 Hesler, Lex R. Apple cankers and their control. Cornell Univ. Agr. 



Exp. Sta. Circ. 28 : 17-28. 1915. 

 Scott, W. M., and Rorer, J. B. Apple leaf spot caused by Sphaeropsis 



Malorum. U. S. Agr. Dept. Plant Indus. Bur. Bui. 121 : 47-53. 



1908. 



