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; asa 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 
44-50 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. Bul. 379: 51-148. 1916. 
Hesler, Lex R. Apple cankers and their control. Cornell Univ. Agr. 
Exp. Sta. Cire. 28: 17-28. 1915. 
Scott, W..M., and Rorer, J.B. Apple leaf spot caused by Sphaeropsis 
i aia U.S. Agr. Dept. Plant Indus. Bur. Bul. 121 : 47-53. 
1908. 
