APPLE DISEASES 



461 



isolated from several kinds of plants have 

 proved easily cross-inoculable artificially 

 to numerous other species in different 

 plant families. More than one orchardist 

 has also had practical proof of cross in- 

 fection through contaminated soil. Con- 

 sequently wise growers will hesitate to 

 risk the chance of transmitting crown 

 gall from one kind of cultivated crop to 

 another by planting susceptible varieties 

 in ground from which plants diseased 

 with crown gall have recently been rooted 

 out. 



In the following paragraphs we give 

 some information regarding the character 

 and seriousness of crown gall as it ap- 

 pears on some of the more important 

 cultivated fruits: 



The Apple 



Upon seedlings and root-grafted trees 

 in the nursery we find principally the 

 hairy root condition or galls of a some- 

 what fleshy nature. (See Fig. 2, A and 

 B. ) On older trees the persistent peren- 

 nial hard galls are more frequent and in 

 the orchard there appears also upon the 



trunks and branches an aerial form of 

 the disease. Aerial tumors are rarer than 

 the root or crown form in most localities. 

 They are characterized by the growth 

 of smooth, woody, persistent swellings, 

 which later become warty from the ap- 

 pearance of numerous stubby roots which 

 break out just to the surface. It is not 

 possible for us to state at present exactly 

 how these aerial tumors originate, but 

 the causal organism is similar to that pro- 

 ducing other forms of crown gall. 



Crown gall and hairy root are very 

 prevalent in the nurseries, and because 

 of laws forbidding the sale of trees affect- 

 ed with this contagious disease, the an- 

 nual loss to nursery men is very large. 

 Unscrupulous dealers sometimes cut off 

 the galls and sell the trees, but tumors 

 may reappear on such trees. Certain pre- 

 cautions may be adopted, however, in the 

 care of young trees and in the methods 

 of grafting which will reduce greatly the 

 amount of disease in the nursery. t 



: See Bulletin 1G8. Bureau of Plant Industry, 

 U. S. Department Agriculture. 



Fig. 2. A, Cionn Gall on Young Apple Tree. B, Hairy Koot on Young Apple Tree. 



