Table 1. Threshold captures of leafminer adults on sticky red rectangle traps at tight cluster or pink as 

 prediction of reaching a threshold level of first-generation larvae. 



Number of blocks where 



the adult capture 



threshold was reached 



Number of blocks where 



the adult capture 

 threshold was not reached 



Total 



65 



17 



37 



indicates that 300 mines per 100 leaves (7.5 x 40) dur- 

 ing the third generation of leafminers in August can 

 result in 30% or more pre-harvest drop of Mcintosh in 

 dry years. Studies prior to 1991 provided data that we 

 used to construct tentative threshold cumulative cap- 

 tures of three adults per trunk trap by tight cluster and 

 nine adults per trunk trap by pink as being thresholds 

 that could translate into seven first-generation mines 

 per 100 leaves. 



Results 



For a threshold level of three adults per trap at 

 tight cluster, the results (Table 1 ) show that trunk trap 

 captures reaching or exceeding this threshold correctly 

 predicted the need to spray to prevent mines from reach- 



ing a threshold of seven per 1(X) leaves in 100% of cases 

 (14 of 14). Trunk trap captures not reaching this level 

 correctly predicted the need not to spray in 77% of cases 

 (39 of 51). Overall, trap captures correctly predicted 

 the need to spray or not to spray in 8 1 % of cases (53 of 

 65). 



For a threshold level of nine adults per trap at 

 pink, the results (Table 1) show that trunk trap cap- 

 tures reaching or exceeding this threshold correctly pre- 

 dicted the need to spray to prevent mines from reaching 

 a threshold of seven per 100 leaves in 88% of cases (17 

 of 19). Trunk trap captures not reaching this level cor- 

 rectly predicted the need not to spray in 80% of cases 

 (37 of 46). Overall, trap captures correctly predicted 

 the need to spray or not to spray in 83% of cases (54 of 

 65). 



Fruit Notes, Spring, 1995 



