40O Bulletin 75. 



' ' tips ' ' — which must generally be relied upon in this state for 

 the diagnosis of the 3^ello\vs ; and even the tips, as I have said, 

 may be so little developed as not to attract attention. The one 

 unmistakable and invariable symptom of the peach yellows is in 

 the fruit. 



The fourth and final stage of the disease is that in which the 

 entire tree assumes the narrow, yellow or reddish and rigid leaves, 

 and in this condition the tree is not readil}- distinguished, by the 

 novice, from trees which are much debilitated by borers or neglect. 

 The length of time from the onset of the disease at which this 

 final stage and the death of the tree occur, is not a fixed period. 

 It is undoubtedly modified by many conditions. From the time 

 when the first symptoms appear, it is not less than three years 

 before death occurs, and it is oftener five or six j^ears. But death 

 is sure to come sooner or later, for there is no indisputable case on 

 record of yellows having been cured. 



There is abundant proof that yellows is communicable from tree 

 to tree. Sooner or later, every peach tree in any community in 

 which the disease appears, may be expected to die from it, unless 

 rigorous measures are taken to keep it in check. The disease is 

 so insidious and often so slow in its progress that it usually be- 

 comes thoroughly established in a community before it attracts 

 attention, and peach growers generally procrastinate in applying 

 restrictive measures. It is unknown how the yellows spreads, but 

 it is not through the soil, for young trees may be set wdth safety 

 where 3'ellows trees have been removed. Neither is it always, if 

 ever, conveyed from flower to flower, for trees which have not yet 

 blossomed often contract the disease. It does not inhere in the 

 roots, for trees grafted upon plum stocks contract it. There is 

 every reason to believe, also, that it is not carried on pruning 

 tools. The means by which the disease spreads will probably not 

 be known until the cause of the trouble is ascertained. Respect- 

 ing this cause, there has been distinct progress in eliminating 

 almost every origin which has been ascribed for the disease. It is 

 known that yellows is not due to conditions of soil or climate, to 

 mechanical injuries, to over-bearing or starvation, to methods of 

 propagating, pruning or cultivating, to insects or fungi, and Dr. 

 Erwin F. Smith, of the national Department of Agriculture, who 



