12 MASS. EXPERIMENT STATION BULLETIN No. 285 



the following day. There was some curculio activity. This was followed by eight 

 days of cool, rainy weather with maximum temperatures below 70° F., which 

 reduced curculio activity to a minimum. The warm weather of May 22 and 23 

 promised to be the beginning of a period of great curculio activity, but the dura- 

 tion of the high temperatures was so short that comparatively little feeding took 

 place in the orchard. On June 1 the maximum temperature was 75° F., and it 

 continued above 80° F. for seven days, with a maximum of 94° F. on June 5. 

 The majority of the curculio activity took place in that period. Because of the 

 long period of unfavorable weather preceding, the majority of the fruit growers 

 sprayed during the early part of the warm period from June 1 to 8, and the best 

 control of this pest in recent years was obtained. 



Figure 4 also shows that the critical period in curculio activity, in respect to 

 high temperature, did not occur in 1930 until June 1 to 8, 12 to 14 days after the 

 calyx application. Although there was little curculio activity during the cool 

 weather from May 19 to June 1, there was a gradual accumulation of curculios 

 in the trees and these were stimulated to considerable activity by the first high 

 temperatiu"es. Therefore, the dividing line between timely control treatments 

 and late treatments was June 2. 



Orchard Control in Relation to Time of Application 



The practical application of these temperature studies is evident in an analy- 

 sis of the records of blemishes on harvested fruit taken by Mr. Fred E. Cole of 

 the Worcester County Extension Service, and Mr. John C. Handy of the Middle- 

 sex County Extension Service, in connection w^ith their County Fruit Pest 

 Survey, and the State 90 Per Cent Clean Apple Club Project. These orchards 

 had a crop of at least 300 bushels of one variety, and the spray was carefully 

 applied from a commerical standpoint. The materials used were approximately 

 the same in each case, and with few theoretical exceptions the difference in con- 

 trol is due to the time of application. 

 Worcester County, 1930 



In 1930, the Worcester County records for 29 orchards show that 11 per cent 

 better control of the plum curculio on Mcintosh apples, and 14 per cent better 

 control on Baldwin apples, were obtained bj^ spraying from May 28 to June 2, 

 than when the spray application was made later. No sprays were applied on 

 May 30 and 31 because of unfavorable weather, and these dates are omitted in 

 Table 7. 



Table 7. — Percentage of Harvested Apples Injured by Plum Curculio. 

 Worcester County, Mass., 1930 



Time of Application 



Infestation, Per Cent 



May 28, 29, June 1,2 

 June 3, 4, 5, 6, 7 



Climatic Conditions Influencing Control in 1931 



In 1931 the critical period in curculio activity in respect to temperature 

 came 4 to 6 days after the calyx spray was applied in most orchards, and extended 



