1 lb/100 gal was applied on June 5 and 27 for plum 

 curculio control and Mitac™ 1.5 EC was applied at 1.5 

 pts/100 gal on July 17 and 24 and on August 9 for pear 

 psylla. 



Safer Insecticide Concentrate at 2 gal/ 100 gal was 

 applied to the treatment block on May 20, July 24, and 

 August 9 and 22 for pear psylla. No untreated check 

 trees were included in this study as previous experi- 

 ence has shown that psylla will reach significant out- 

 break levels in this block in the absence of any summer 

 control sprays. 



The clumped distribution of active stages of psylla 

 resulted in high statistical variability within treatment 

 blocks. This variability in turn contributed to lack of 

 statistically-significant differences between treat- 

 ments even when population trends appeared to differ, 

 e.g., on June 29 and July 29 (Figure 1). 



Significantly greater numbers of late instar psylla 

 nymphs were noted in the soap block at petal fall. An 

 initial soap treatment on May 26 effectively reduced 

 psylla numbers to levels comparable to trees destined 

 to receive Mitac treatments. 



Soap-treated trees again had significantly greater 

 psylla levels on July 18; however, Mitac was applied on 

 July 17, without a corresponding application of soap. 

 In spite of this, early instar psylla numbers in the soap 

 treatment exhibited a downward trend on July 24, 

 while similar stages in Mitac trees had rebounded to 

 their highest levels. Trees treated with soap had 

 significantly more early instar nymphs than Mitac- 

 treated trees on August 21, 12 days after an application 

 of Mitac. The fourth soap application on August 22, 

 with no corresponding Mitac spray, effectively reduced 

 psylla numbers through the rest of the season. 



Early instar psylla numbers in Mitac treated trees 

 had reached outbreak levels again on August 25, when 

 pre- harvest considerations would allow no further use 



ofamitraz. In an adjacent pear block at the HRC where 

 a similarly increasing psylla population was noted, 

 soap was used effectively during the pre- harvest period 

 to reduce psylla infestations below acceptable levels. 



Perhaps due to this late psylla outbreak, noted 

 above, treatment blocks did not differ significantly with 

 regard to sooty mold on fruit at harvest (8.7% and 

 11.0% for Safer's- and Mitac-treated blocks, respec- 

 tively). However, 50% of soap-treated fruit, compared 

 to none of the Mitac-treated fruit, exhibited the dark 

 surface lesions (fruit phytotoxicity) which we observed 

 in our 1987 trials and which have been reported in the 

 Hudson Valley. We view such lesions as a major 

 drawback to the use of soap sprays, as they contribute 

 to fruit downgrading. We are presently unable to 

 provide any information regarding the precise condi- 

 tions which contribute to phytotoxicity, or the steps 

 which may be taken to alleviate it. 



We conclude that if insecticidal soap is integrated 

 into a psylla control program sufficiently early, i.e. as 

 psylla numbers begin to reach outbreak levels, its use 

 represents an effective psylla management alternative 

 to other summer spray materials. In our trials, four 

 soap applications costing $41.41/acre provided control 

 of pear psylla equivalent to three applications of Mitac 

 costing $15. 75/acre. However, unless progress toward 

 reducing fruit phytotoxicity can be achieved, low yields 

 of blemish-free fruit may deter use of insecticidal soap 

 sprays by even those growers who might otherwise 

 accept its higher cost. 



Acknowledgments 



We wish to thank Safer, Inc., for donating the 

 material for our 1989 trials and Mary Ellen Ahearn for 

 technical assistance. This project was funded through 

 the Massachusetts Department of Food and Agricul- 

 ture Competitive Grant Program. 



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Fruit Notes, Spring, 1990 



27 



