208 



THE NURSERY-MANUAL 



The spots are first small, but they increase in size to a half 

 inch in diameter. Often a number of spots coalesce involving 

 a considerable part of the leaf tissue. A very marked char- 

 acter is the fringed border of the spots. Severely affected 

 leaves usually turn yellow and fall prematurely. 



Cause. The cause of the disease is the fungus Diplocarpon 

 roses. Spores of the fungus which are borne in the black spots 



on the leaves are disseminated 

 by wind and rain to new fo- 

 liage where they produce 

 new infections. Special fruit- 

 ing bodies which develop in 

 the diseased leaves that fall 

 to the ground carry the fungus 

 over winter. 



Control. Bordeaux mix- 

 ture, or a dust mixture con- 

 sisting of 95 parts finely 

 ground sulfur and 5 parts 

 powdered lead arsenate, will 

 control the black-spot dis- 

 ease. The first application 

 should be made in early sum- 

 mer, soon after the first new 

 leaves are developed. Four or five subsequent treatments 

 should be made at intervals of about two weeks. 



MILDEW OF ROSE AND PEACH. Mildew is found on both 

 the peach and the rose, but it is commoner on the latter. As 

 a rule, peach mildew is of little importance in the nursery, but 

 rose mildew often causes considerable damage. The disease 

 on roses checks the growth of the plants in the field, and some 

 growers are of the opinion that severely mildewed rose stock 

 does not keep well in storage. The affected shoots tend to 



FIG. 220. Black-spot of rose. 



