TREATMENT FOR CONTROL OF APPLE APHIDS. 53 



Discussion of Results. 



Efficiency of Lime-sulfur against the Aphids. — It is evident from the 

 foregoing that Ume-sulfur alone appUed at the delayed dormant period 

 even at full dormant-season strength is practically worthless in con- 

 trolling apple aphids. Actual count shows this material to be under 10 

 per cent, efficient, and in every case the delicate, recently hatched aphids 

 were the onlj^ ones affected. In addition to those killed, a few were more 

 or less permanently incapacitated, judging from their feeble condition, 

 but even if these were included in the "kill," it would alter the results 

 given only slightly. The count to determine the number of plant hce 

 killed was made at later periods of the day on which treatment was 

 applied and on subsequent daj-s until all deaths due to the treatment 

 could be checked up. It should be kept in mind that all the twigs were 

 thoroughly dipped and that the ordinary orchard spraying would prob- 

 ably be even less effective, unless perhaps the apphcation of the spray 

 under pressure might possibly dislodge some of the plant Uce and thus 

 counterbalance the less thorough application. Observations made after 

 treatment showed that the older plant lice were apparently unaffected 

 and were quietly feeding, except where the coating or drying out of the 

 buds by the lime-sulfur made it necessary for them to seek suitable feed- 

 ing places elsewhere. 



Action of Lime-sulfur upon the Aphids. — The action of the lime-sulfur 

 upon the j'oung plant lice, the only stage of the active insects against 

 which it appears to have any particular effect, seems to be mainly me- 

 chanical, in that it sticks these delicate young to the twigs in such a 

 manner that death is probably the result of starvation. Death occurred 

 very slowly in some cases, since the insects were often found feebly 

 struggling to liberate themselves several hours after the treatment. 



Foliage Injury by Lime-sulfur. — The effect of the lime-sulfur upon the 

 opening foliage was noted both in the laboratory and upon field-sprayed 

 trees, where more rehable data of this nature could be obtained. While 

 a number of elements may enter in to affect results, such as the variety 

 of apple, weather conditions, pressure under which the apphcation is 

 made, etc., our tests showed that little or no eventual injury results from 

 the use of dormant-season strength lime-sulfur where the buds have not 

 expanded beyond a half inch. Upon sprayed trees, where expansion 

 beyond this point had occurred, injury was more evident, but even on 

 treated trees, with the foliage out three-fourths of an inch to an inch or 

 more, an examination several weeks after application showed Httle other 

 than tip injury in most cases. It seems advisable, however, from the 

 standpoint of thoroughness if for no other reason, to confine such spray- 

 ing within the delayed dormant period. It was noted that the long 

 pubescence on foliage that had expanded to about half an inch, but had 

 not unfolded to any extent, appeared to shed the lime-suLfur readily or 

 absorb it only in occasional spots, which resulted in injury at these 



