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Mcintosh Red Del. 



Russetting 



Mcintosh Red Del. 



Insect Damage 



Figure 6. Percent damage to fruit, assessed at harvest. Insect damage includes that from leafrollers, 

 tarnished plant bug, and codling moth. Means within cultivar were not significantly different unless noted; 

 where noted, means labelled by different letters are significantly different at odds of 19 to 1. 



result cannot be explained biologically. Other treat- 

 ments did not differ with respect to scab injury. 



Evidence of phytoxicity was present on fruit from 

 all Safer's-treated blocks (Figure 6) in the form of 

 russet-colored rings, a spray-burn. Rings generally 

 formed on the calyx end of Delicious and the shoulder 

 of Mcintosh. On Delicious apples, russetting was 

 greatest where higher rates of soap were applied, while 

 on Mcintosh, russetting was not related to rates of ap- 

 plication. 



Conclusions 



This study demonstrates that Safer's Insecticidal 

 Soap is an effective miticide when compared to Omite. 

 In our tests, soap was not as effective as Thiodan 

 against aphid populations. Aphid populations treated 



with soap were not sufficiently reduced and they re- 

 bounded much faster than did those treated with 

 Thiodan. There was little difference among treatments 

 with respect to their effects on aphid predator densi- 

 ties, although the low rate of insecticidal soap appeared 

 to be less toxic on syrphid larvae. 



An important concern in the use of insecticidal 

 soap is the severity foliar phytotoxicity exhibited by 

 Delicious, and the spray burn russetting on fruit that 

 occurred on both cultivars in our trials. This fruit dam- 

 age is apparently only cosmetic, but under current 

 grading standards it would result in a reduction of 

 value of the crop. Before insecticidal soap becomes a 

 useful apple orchard tool, it will be necessary to deter- 

 mine on which cultivars soap is phytotoxic, and under 

 what conditions such injury can be avoided. 



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Fruit Notes, Spring, 1990 



25 



