Table 3. Cost per acre 

 Research Center, 1980-87*. 



of spray materials, Block C, Horticultural 



*Based on 300 gal/acre dilute base and non-discounted chemical costs. 



It is interesting to note that although apple 

 maggot flies were caught in the block, no AMF 

 injury was ever detected. In the case of mobile 

 pests like the AMF, which normally do not 

 establish resident populations in sprayed blocks, 

 orchard edges typically experience more pest 

 pressure than interiors. We have looked at 

 hundreds of fruit in Block C over the years, and 

 we have never seen a single fruit damaged by 

 apple maggot egglaying. While it is true that 

 Block C is an interior block, this points out the 

 possibility that growers may be applying more 

 insecticide than is needed in similar blocks 

 elsewhere. The protection afforded interior 

 blocks such as Block C by sprays applied to 

 surrounding sprayed blocks may allow some 

 growers to achieve signiHcant decreases in 

 pesticides required for acceptable pest control. 



Pesticide costs and potential for further 

 reduction (Table 3). By better using spore 

 maturity and weather monitoring and by including 

 SI fungicides against apple scab, we believe that 

 fungicide costs can be reduced further. This past 

 year, Rubigan^"* allowed longer spray intervals 

 between appUcations during frequent wetting. It 

 also gave us the confidence to wait until after an 

 infection period had occurred before making an 

 application. Additionally, information was 



available from both a Reuter-Stokes scab 



predictor and a modified hygrothermograph. 

 Having reliable weather information and a 

 fungicide with 96 hours post-infection activity 

 reduced the perceived risk. 



Without Isirge-scale use of red sphere AMF 

 traps, it is unlikely that further significant 

 reductions in insecticide use can be achieved, so 

 that Uttle additional cost saving compared to 

 pre-IPM levels is expected. However, simply 

 reducing the total pesticide load in an orchard 

 should enhance the survival of mite predators 

 and reduce the difficulty of mite pest 

 management. Because of the importance of 

 spider mite pests, oil is an essential component 

 of apple IFM, and will remain a more or less 

 fixed cost. Of course, fluctuations in the price 

 of oil could significantly increase the cost of 

 annual treatment, as in 1980-81. The use of 

 mite predator releases in the future may provide 

 a way to apply oil only every 2 or 3 years, and 

 hence reduce the cost of this material. 



The cost of aphicide would not be expected 

 to increase in low-spray blocks, due to enhanced 

 survival of aphid predators. Proper tree pruning 

 and fertilization will help deter aphid buildup 

 beyond economic thresholds. However, 



occasional outbreaks (rosy aphid) could require 

 aphicide use. 



11 



