Effects of Pesticides on Pest Ecology in 

 Blocl<s of Scab-resistant Apple Cultivars 



Daniel R. Cooley 



Department of Plant Pathology, University of Massachusetts 



Ronald J. Prokopy, Jennifer Mason, and Starker Wright 

 Department of Entomology, University of Massachusetts 



We have described previously our attempts to elimi- 

 nate orchard applications of insecticide and miticide after 

 early June and to limit the use of fungicide over the entire 

 growing season, utilizing second-level IPM and scab-re- 

 sistant cultivars [Fruit Notes 59(1): 8-12, 1994]. This ap- 

 proach may allow the increase of natural enemies of ar- 

 thropod pests to provide significant biological control. It 

 also may slow rates at which pests develop resistance to 

 pesticides and minimize potential risks from pesticide resi- 

 dues on fruit at harvest. 



The study detailed here differs from those of second- 

 level IPM (see earlier article in this issue ) in that scab- 

 resistant apple cultivars (SRCs) are used, rather than com- 

 mercial cultivars. Presently the commercial acceptance of 

 SRCs does not make them suitable for wide-scale planting; 

 however, small plantings may serve very limited markets. 

 In addition, these plantings provide sites which allow us to 

 study the effects particularly fungicides on the orchard ecol- 

 ogy, since fungicides directed at scab can be eliminated 

 from the pest management program without affecting tree 

 and fruit development directly. We are particularly inter- 



ested in the effects that fungicides may have on mites and 

 insects. 



In our earlier article we described our reasons for sus- 

 pecting that fungicides may increase pest mite populations. 

 We know that one fungicide, benomyl, can sterilize preda- 

 ceous phytoseiid mites. We also know that there are natu- 

 rally-occurring fungi which can infect and kill msects and 

 mites, and that these fungi may be inhibited by fungicides. 

 While the mechanism behind fungicide effects on mites is 

 only crudely understood, work in Vermont confinns that 

 eliminating fungicides from an orchard can stimulate mite 

 biocontrol. 



Unfortunately, eliminating fungicides in SRC blocks 

 comes with a few problems. Last year, elimination of fun- 

 gicides combined with second-level arthropod management 

 in blocks of SRCs produced fruit with acceptable levels of 

 arthropod damage, but not of flyspeck and sooty blotch, 

 which affected 1% and 4% of the fruit, respectively. In 

 blocks under standard fungicide management, the damage 

 levels were only 0.1% and 0.4%, respectively. In addition, 

 work in New York has shown that elimination of fungi- 



16 



Fru/t Notes, Winter, 1995 



