10 



MASS. EXPERIMENT STATION BULLETIN No. 285 



when its adhesiveness is aided by a spreader or sticker, would persist in its max- 

 imum efficiency for several days, but experiments (4) have shown that the sur- 

 face area of the apple increases 6 per cent or more per day during this period of 

 growth, with a proportionate increase in the unprotected area of fruit. It is, 

 therefore, possible for about one-third of the surface of the apple to be free from 

 poison 5 days after spraying, and the curculio beetles are quick to take advantage 

 of these unpoisoned areas on the young fruit. The physical force of the spray 

 when applied causes the curculio beetles to fall from the tree as is their habit 

 when disturbed in any way, and apparently it is more difficult for them to find 

 an unpoisoned area on the apple when they return to a recently sprayed tree. 

 Where there may be some delay in treating the complete orchard, it is advis- 

 able to spray first that part of it which is adjacent to woods, stone walls and 

 brush, or other suitable winter cover where the beetles will congregate first. It 

 is also advisable during periods of maximum activity to spray first those varieties 

 which are most susceptible to curculio injury. Previous experiments (9) have 

 shown that apple varieties which bloom earliest and grow most rapidly imme- 

 diately after petal fall are the first to provide suitable locations for feeding and 



Figure 3. — Occurrence of Overwintering Plum Curculios in the Trees in 



Relation to Maximum Daily Temperature. 



Waltham, Mass., 1931 



- 90 



V80 



70 K 



-60 



-50 



/6 19 20 ei 22 23 24 25 26 27 28 29^0^1 I 2 v) V 5 6 



MAV JUNE 



