PEACH YELLOWS. 387 



SPREAD OF THE DISEASE BY INFECTED PRUNING KNIVES OR SAWS. 



Many persons have asserted that the disease may be propagated in this way. 

 I have no positive evidence on this point; and no experiments have yet been 

 undertaken to settle it, owing to the great amount of work involved in the 

 other examinations and experiments here set forth. 



This experiment should be tried carefully on registered limbs in an unin- 

 fected district, or if in an infected one then in a larger number of trees and 

 in as healthy an orchard as can be found. 



NURSERIES NOT RESPONSIBLE FOR ALL OF THE OUTBREAKS. 



On other grounds than those already set forth, I am confident that neither 

 sound stocks nor healthy buds wJl entirely protect from yellows. The disease 

 does not all come from the nursery. It must have some other means of dis- 

 semination. The following are my reasons for this belief : 



1. In the infected districts I could not satisfy myself that the trees of one 

 nurseryman were more subject to yellows than those of another, although I 

 took great pains in many instances to trace the history of the trees, especially 

 if they were young ones. 



2. Some experiments with stocks and buds of a known character seem to 

 show this quite conclusively. In orchard No. 11 of this report special pains 

 was taken to secure healthy trees. This orchard was budded and planted by 

 Walter Morris, cashier of the Farmers' Bank, Dover, Del. He procured the- 

 seed from a load of healthy natural fruit, brought into Dover and sold to Mr. 

 Eichardson in a year when there was a great scarcity of peaches. They were 

 budded next year, Mr. Morris selecting the scions himself from a healthy 

 orchard which hung very full of fruit. The yellows first appeared in this 

 orchard about four years ago, i. e., four years after budding, and spread very 

 rapidly in 1886 and 1887. I came across a similar case on the farm of S. H. 

 Derby, near Woodside, Del. Mr. Derby selected the pits himself from a very 

 thrifty-bearing orchard, free from yellows, and cut the buds from healthy 

 trees in an orchard where yellows was unknown and where it did not appear 

 until recently, i. e., within the last three or four years. This orchard contains 

 about 10 acres and is nine years old from the bud. The first premature 

 peaches appeared in 1886, i. e., six years after budding and several years after 

 the orchard had fruited. In 1887 I saw many diseased trees in this orchard, 

 and there were new cases in 1888. 



3. The fact that orchards frequently make a vigorous early growth and 

 then bear peaches for fifteen or twenty years, often in enormous quantities, 

 before showing symptoms of yellows. 



It seems almost impossible to believe that trees, which are the picture of 

 health when young, and which continue to appear vigorous for three or four 

 years, contain within themselves, in a dormant state, all the elements of 

 disease, yet such is the case, if the yellows is propagated only by diseased stocks 

 and buds. For the sake of argument, in the absence of direct proof to the 

 contrary, it may be admitted that trees which premature their first fruit have 

 in every instance been diseased from the beginning, no matter how healthy 

 they appeared to be. But what shall we say of trees which succumb after hav- 

 ing borne several crops of healthy peaches? It is extremely doubtful wh'-ther 

 such trees contracted the disease in the nursery. Finally, it passes the bounds 



