CHAPTER XXXIV 

 SPRAYING AND DUSTING FOR LEAF DISEASES 



In the absence of experimental data on the spraying or dusting 

 of shade and ornamental trees for the control of leaf diseases, 

 only very general recommendations can be made. The various 

 leaf-spots, powdery mildews and sooty molds that often affect 

 trees doubtless can be controlled by fungicides applied to the 

 leaves. General directions will be found under the discussion 

 on the powdery mildews for the control of these fungi (see 

 page 37). These recommendations are based largely on the 

 results obtained in controlling powdery mildews on fruits and 

 small ornamentals. In order to control the many leaf-spot 

 diseases, data should be available on the life history of the patho- 

 genes (so that the time of applications might be determined), 

 the strength and type of fungicide to use and the number of 

 applications that are necessary. Without a definite knowledge 

 of these facts, spraying can only be advised as an experimental 

 practice. 



The source of primary infection in the spring for most leaf- 

 spot diseases is in the old dead leaves on the ground. These 

 should be raked together and burned in the late autumn. Some 

 of the leaf-spot fungi also attack the twigs and when this is the 

 case the diseased twigs should be pruned off. Unless these 

 eradication measures are taken, spraying will be less successful 

 in controlling the disease. 



The three common fumgicides are bordeaux mixture, lime- 

 sulfur solution and sulfur dust. The toxic agent in the first is 

 copper and in the latter two, sulfur. These substances are ap- 



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