Crown-Gall of Apple and Peach 5 



Recently, experimental data have been published on crown-gall experi- 

 ments with apples, from the States of lowa^ and Montana.'^ The ex- 

 periments were planned and executed on a large scale. In Montana it 

 appears that while there was no noticeable effect on the vigor of the 

 trees, nevertheless the root development of galled trees was not good, 

 and it is thought that this would have become apparent when the trees 

 began to bear heavy crops. In Iowa numerous growth data were recorded, 

 and these show without exception that galled trees did not grow so fast 

 as did trees free from gall. It should be noted, in this connection, that 

 the method employed was one which has not yet received general indorse- 

 ment by horticulturists. 



An objection to all the experiments reported, including the one about 

 to be recorded, is that the real test comes only with the production of 

 fruit (because the trees are grown for the fruit they bear, not for the wood 

 thej^ produce). A well-planned experiment to determine the effect of 

 crown-gall should extend well into or through the life of the plant. This 

 would be a very long time for apple trees, but could be done relatively 

 easily with peaches. 



A proper interpretation of any of the crown-gall experiments thus far 

 reported is rendered difficult by the fact that the experimental trees used 

 have consisted of a miscellaneous collection for which there are no data 

 as to original source, particularly as to the exact character and origin of 

 the stock on which the trees were grown. The Iowa experiments illustrate 

 this very well. One of the conclusions of Greene and Melhus is that 

 Wealthy is more susceptible to crown-gall than is Jonathan. It is difficult 

 to understand how this can be, since the varieties were grafted on seedling 

 stock and an examination of the illustrations indicates that the galls are 

 confined almost entirely to the stocks. It thus becomes necessary to 

 assume an influence of scion upon stock which is not yet admitted by 

 horticulturists. Under the circumstances it may be assumed with equal 

 probability that the conditions of the experiment were such that a large 

 variable factor was not brought under control. The Iowa experiment 

 is further compHcated by the fact that the plot of land in which the 

 trees were planted had grown nursery stock some of which was affected 

 with crown-gall, and that the plot is so located that it, or at least a part 

 of it, received the wash from adjacent affected trees. Furthermore, the 

 report does not state whether the trees were planted in such a way as to 

 eliminate variations in soil and in growth conditions. It must be remem- 

 bered in this connection that in average orchard planting the chance of 

 infection after the trees are permanently set is very small. 



' Greene, Laurenz, and Melhus, I. E. The effect of crown gall upon a young apple orchard. Iowa 

 Agr. Exp. Sta. Research bul. 50: 145-176. 1919. 



» Swingle, D. B., and Morris, H. E. Crown-gall injury in the orchard. Montana Agr. Exp. Sta. Bul. 

 131:123-139. 1918. 



