128 



N. H. AGR. EXPERIMENT STATION 



[Bulletin 144 



CROWN GALL. 



Pseudomonas tumefaciens. Erw. Smith and Townsend. 



Crown gall is the term applied to abnormal outgrowths near 

 the surface of the soil in the region of the collar. It occurs on 

 practically all the stone, pomaceous and bush fruits. With most 

 of these plants the disease has been proven to be contagious. 

 Attempts to produce the disease by inoculation on healthy apple 

 trees have usually been unsuccessful. Affected apple trees should 

 be regarded with suspicion, however, and great care taken to 

 reject all diseased plants at the time of transplanting. The dis- 

 ease usually does the greatest damage on nursery stock. 



EUROPEAN APPLE CANKER. 



Nectria ditissima Tul. 



This disease is reported as serious in the 

 orchards of Europe, and is apparently be- 

 coming widely distributed in America. 

 It is not of so common occurrence in New 

 Hampshire as the black rot canker, but is 

 more destructive where found. The fungus 

 seems to be dependent upon wounds for 

 entrance to the host tissue. It attacks the 

 inner bark and the cambium, and to some 

 extent the young wood. The mycelium is 

 perennial in the host. As the new growth 

 develops around the wound it is attacked 

 and killed by the fungus; thus a series of 

 ridges may be developed, giving a charac- 

 teristic appearance to the disease (Fig. 

 26). 



Two kinds of summer spores are pro- 

 duced, the first small and unicellular, the 

 sc-cond sickle-shaped and having three or 

 more cells. The latter are probably largely 

 responsible for the spread of the disease during the summer. In 

 the spring compact clusters of red lemon-shaped perithecia may 

 be found near the edge of the canker. These may be seen with 



Fio. 26. — European Apple 

 Canker. 



