360 Fruit-growing in Arid Regions 



ment of Agriculture, published a brief account of their work with 

 galls on the Paris daisy. They proved that this particular gall 

 is caused by the attacks of a bacterium, and, what is more im- 

 portant, they found that when pure cultures of this organism 

 were inoculated into peach roots, galls were formed that resemble 

 closely the common crown-gall. 



So it appears that we are at last to have the cause of crown- 

 gall explained. But in the meantime we know that under semi- 

 arid conditions this disease is often fatal to all kinds of orchard 

 trees. We also think that it is spread in the orchard from tree 

 to tree, although this has not been proved. No remedy has yet 

 been suggested which has any value in controlling the disease. 

 The only thing that can be suggested is to insist on the most 

 rigid inspection of nursery stock, and all trees should be rejected 

 that show any traces of gall. All orchard trees found to be dis- 

 eased should be destroyed, particularly apple trees, as they rarely 

 live over ten years, and what fruit is borne is likely to be under- 

 sized. 



Mildew (Podosphcera species). A mildew similar to the disease 

 that attacks the peach is found occasionally on apple twigs. 

 This has not been serious as yet, but if at any time it should 

 need attention, spraying with bordeaux mixture as outlined for 

 peach mildew will be effective. The young, vigorous twigs, 

 young trees, and grafts are most subject to attack. 



Root-rots. Orchardists and experiment station workers 

 alike have been puzzled for several years over the cause of root- 

 rot in apple and pear trees. The name conveys at once the 

 condition in which the trees are found. In some cases no injury 

 is to be seen above ground, but when the tree dies, it will be found 

 to be girdled just below ground, and most of the roots are decayed. 

 In other cases strips of dead bark extend up the trunks and 

 often into the larger branches. In such cases the first indica- 

 tion of disease is the appearance on trunks and branches of dark 

 brown spots caused by the exudation of sap. As the disease 

 progresses, the bark dries down to the wood, all of the involved 

 part taking on the dark color. Such trees usually ripen their 

 foliage early in the fall, and the bark of the branches has a pecul- 



