DISEASES OF ROSES 97 



Cause. Crown-canker of the rose is caused by the fungus 

 Cylindrocladium scoparium. This organism was first reported 

 from Ohio where it was found growing saprophytically on a pod 

 of the honey-locust. Later it was found li\ang on dead paw-paw 

 leaves. The writer described the fungus as a parasite on the rose 

 in December, 1917. 



Although spores of the fungus have never been found by the 

 writer on plants growing in the benches, they frequently develop 

 in from two to five days on diseased rose plants when kept in a 

 moist chamber. Consequently they are probably formed in the 

 greenhouse on plants growing under moist conditions. Spores 

 placed in water germinated after three to twelve hours. They 

 are thin walled and probably not long lived. Just what part they 

 play in disseminating the fungus is unknown. Infection of plants 

 is readily obtained by spraying them with water containing viable 

 spores in suspension. 



Moisture Relation. 



Moisture apparently plays an important role in the severity of 

 the disease. Lesions on stems well above the surface of the soil 

 resulting from artificial inoculations appear to dry and make no 

 further progress unless kept moist by being surrounded with wet 

 cotton or some such substance. Inoculations made at a point 

 several inches above the soil frequently result as above. One 

 grower who has had considerable experience with crown-canker is 

 of the opinion that the disease is lessened by placing plants with 

 the graft union above the soil, thereby preventing infection at this 

 point. The same grower stated that the seriousness of the disease 

 is reduced by pulling the soil away from the crown of the plant, 

 thus creating a more dry condition at this point. These are un- 

 desirable methods, for grafted plants usually develop roots at the 

 graft union when planted sufficiently deep. It is the opinion of 

 the writer that the fungus is low in parasitism and that conditions 

 of moisture are important factors in its development. 



Control. Although experiments are under way in the hope of 

 developing some method of controlling the crown-canker of rose 

 no definite results are yet at hand. From the nature of the fungus 



