August, '12] BACK AND PRICE: STOP-BACK OF PEACH 333 



typical Stop-back in the laboratory, six specimens of pratensis were 

 placed in a rearing cage with seven shoots of peach on June 3rd. By 

 June 7th. all shoots had developed typical Stop-back. The bugs were 

 closely watched at intervals and were seen to puncture the terminal 

 buds. Check shoots developed no Stop-back. 



Stop-back has never been abundant enough to attract much atten- 

 tion at Blacksburg during past years. To produce typical Stop-back 

 in a block of nursery trees showing but slight affection from this 

 trouble, two cages were placed over trees after a manner similar to that 

 at Richmond with the following results: 



Cage No. 10. June 10. Caged five non-affected trees; all bugs excluded. 



June 17. No Stop-back has developed. 



Cage No. 11. June 10. Caged five non-affected trees; eleven bugs placed in cage. 



June 13. Terminal buds of main shoots wilted. 



June 17. No examination made since the 13th. All terminal buds of main shoots 

 affected and blackened. Comparatively few terminal buds of the large number of 

 lateral affected. 



From the above experiments, the writers believe that there is no 

 room for doubt regarding the causative agent of Stop-back of peach, 

 at least in Virginia during the season of 1911 and 1912. The fact 

 that they could produce Stop-back at will in field and laboratory by 

 using Lygus pratensis and were never able ,to find Tarsonemus waitei 

 in even what could be called slight numbers, at a time when the trees 

 were being injured most, warrants this conclusion. And they believe 

 that there is sufficient evidence in published statements to lead one to 

 seriously doubt the conclusions drawn by others regarding T. waitei, 

 unless very different conditions exist in other states. 



The only experimental evidence thus far presented is that given by 

 Mr. Phillips.^ Since Mr. Phillips did not state whether he covered 

 the plants about which he placed affected shoots, and since L. pratensis 

 is knoAvn to occur at Blacksburg, there is no assurance that mites 

 caused the subsequent injury. That too few specimens of pratensis 

 have been found by observers to cause them to disregard it as the 

 causative agent does not appear to have much weight, inasmuch as 

 pratensis appears in large numbers in a comparatively short time, 

 does its greatest damage and then largely disappears. Had the Avriters 

 made their observations during June rather than May of this year, 

 they would have been at as great a loss to know the cause of Stop-back 

 as they were during 1911. Most growers, especially men who have 

 charge of a large acreage, do not notice injury of the nature of Stop- 

 back until it is far advanced and by the time an expert is called upon, 

 the injury is done and the bugs largely gone. As in the examina- 

 tion of newly affected buds, no mites have been found while more 



'Fifth Report, Va. State Ent. & Plant Path., 1906, page 50. 



