EXPERIMENT STATION BULLETINS. 453 



Injury to foliage and flower buds. The strong lime-sulphur, 63^-50, applied 

 just before the blossom buds separated or any time during the cluster stage 

 caused considerable injury to the first leaves in nearly every instance but this 

 injury was never permanent and it was not possible to tell by a casual exami- 

 nation after the blossoms had dropped that any such injury had occurred. 



In some orchards considerable injury occurred on the blossom buds and 

 in others there was very little of such injury. There seemed to be a varietal 

 difference in susceptibihty to such injury; Kieffer apparently being the most 

 susceptible. This difference may have been more apparent in some instances 

 than actually existed as Kieffer blooms earlier than most varieties and the 

 application was usually timed by most growers for an average of all varieties 

 so that Kieffer was the most advanced and consequently more tender. Low 

 temperatures after the application undoubtedly increased the injury. There 

 were several severe frosts during the period when the buds were expanding 

 and before the blossom buds had opened. Trees which were sprayed before 

 these frosts lost many more blossom buds than trees sprayed after the period 

 of low temperature. One grower sprayed early in the forenoon of a day when 

 the temperature had dropped to twenty-three degrees in the morning. The 

 sprayed trees lost many buds while unsprayed trees did not. There were 

 very few places where the final yield of fruit was seriously reduced in spite 

 of apparently severe injury to blossom buds in the spring. 



Effect of hot, dry weather. The psyllas were greatly reduced in many 

 orchards by a period of hot dry weather which prevailed during July. The 

 final effect was different in various orchards and was probably directly related 

 to the vigor of the trees. In orchards of high vigor and with heavy foliage 

 the setback to the psyllas was only temporary as they developed again in 

 serious numbers in September. In orchards of lower vigor and with sparse 

 foliage, they were reduced to such an extent that they caused little injury 

 later. In the South Haven district they were evidently reduced to insignifi- 

 cant numbers in nearly all orchards as little injury was reported late in the 

 season. 



SUMMARY AND GENERAL REMARKS. 



The dormant application to kill the hibernating adults under conditions 

 prevailing during the fall and spring of 1920-21 was not effective in orchards 

 under observation. (Orchards No. 1 and 2.) 



Two applications, one before blossoming to destroy the eggs and one after 

 blossoming to kill the nymphs, were very effective in some orchards (Orchard 

 No. 3) but in other orchards the same or a greater number of applications 

 was not effective (Orchard No. 1). The failures in the latter instances are 

 probably due to the fact that the applications were not as thorough and com- 

 plete as is necessary for the control of pear psylla. 



In one orchard satisfactory results were obtained from the use of but one 

 application after the petals had dropped with a mixture containing lime- 

 sulphur, lead arsenate, hydrated lime and nicotine sulphate. This demon- 

 strates the possibility under favorable conditions of cleaning out the psylla 

 with summer apphcations. (Orchard No. 4.) 



The thorough use of nicotine sulphate in any one of several combinations 

 will be effective at any time during the summer when the psyllas are in the 

 nymph stage but the summer sprays are not efficient when used against the 

 adults. (Orchard No. 1.) 



Hot and dry weather materially reduces the number of psyllas but later 



