Studies on Eggs of Apple Plant Lice (31 



lime-sulfur 1-9 by itself will kill a large percentage (90 per cent 

 or l^etter) of the eggs, but not enough to rely upon it alone. 

 Furthermore, lime-sulfur alone will kill only a small percentage of 

 the newly-hatched nymphs if they have made their appearance. 

 Therefore, a combined "spray is better, for it will kill a greater 

 percentage of eggs and all the nymphs. 



The time of application is important. In the foregoing dis- 

 cussion on the behavior of the outer layer of the egg it was shown 

 that the egg is most easily killed when the outer shell has split 

 (plate 1, tig. 2-5) and the gn^atest numl>er of eggs show a split 

 (inter shell when tlic nymphs are emerging. With these facts 

 in mind one can get the best results l)y delaying the dormant spray 

 until the fruit buds start to swell and when they first show green. 

 At this stage the eggs of the oat aphis A. aveiut: will be hatching 

 while the eggs of the rosy aphis, A. sorhi, and the green apple aphis, 

 .1. ixjini, will not hatch for 7 to 1-1 days later. The dormant spray 

 will udt injure swollen fruit I)uds (plate 2, fig. B) or those showing 

 short projecting tips of leaves (plate 2, fig. C), while a dormant 

 spray applied when the leaves are distinct and separated (plate 2, 

 fig. D) will burn the foliage of most varieties. Also, the recently- 

 emerged nymphs of the aphides will conceal themselves to a large 

 extent between the separated leaves, and it will be impossible to 

 hit all of them with a contact spray. 



A miscilile oil, "Scalecide" 1-5, has been given a thorough trial 

 in the orchard and at the laboratory, but it has not produced 

 satisfactory results. Some eggs are killed by "Scalecide" and 

 other miscible oils, but we have not used any which give as good 

 control as a combined lime-sulfur and nicotine spray. ^liscible oils 

 containing derivatives of carbolic acid give more perfect control 

 than those which do not possess the same ; however, there is some 

 indication that an amount of acid (2 per cent of the spray) suf- 

 ficient to kill all the eggs may be detrimental to dormant buds. 



Other contact sprays, such as a strong solution of fish-oil soap, 

 combined with nicotine 1-500 or crude carbolic acid 1.5 to 2 per cent, 

 give considerable promise of becoming effective sprays for th(> 

 control of aphides in the egg stage when applied near the time 

 when the nymphs einei-ge. These studies are as yet in the experi- 

 mental stage, conse(|uently, we cannot reconniiend the treatments 

 for orchard spraying. Any soap spray spreads better than lime- 

 sulfur, and for this reason they may prove to be more efficient. 

 Crude carbolic acid or cresol TT. S. P. combined with fish-oil soap 

 will not injure dormant buds, so far as observed. 



Acknowledgement : The author wishes to express his thanks 

 to Dr. T. J. Headlee for the sincere interest shown and the many 

 valuable suggestions received. He is also indebted to Dr. W. A. 



