Pear Psyllo, All Active Stoges 



Pear Psylla, Soft-Shell Stage 



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Pear Psyllo, Hord-Shell Stage 



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Peor Psyllo, Adult Sloge 



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July 8 July 16 July23 Aug 7 Aug 12 Aug 19 



Figure 1. Number of active stages of pear psylla on check, Safer soap-, and amitraz-treated Bartlett pear trees. 



shells continued to develop), in practical terms, psylla 

 populations under both spray treatments likely were below 

 most growers' "visual action threshold" through harvest. 

 Nonetheless, in blocks where psylla build up earlier in the 

 season, further applications of soap and amitraz likely 

 would be required. 



Numbers of psylla adults (Figure Id) also were 

 reduced significantly by both soap and amitraz. Because 

 adult numbers were significantly higher in amitraz plots on 

 July 23 (pre-treatment), it can be argued that amitraz 

 performed better than soap against this stage. The residual 

 effect of amitraz compared to non-residual soap could 

 account for this apparent difference. 



Although check terminals were infested com- 

 pletely and showed honcydew and sooty mold growth as 

 early as August 7, at harvest only a few fruit from check 

 trees showed signs of honeydew. While no evidence of 

 spray toxicity to foliage was noted in this trial, 49% of Safer- 

 treated fruit were found to be injured at harvest. Phytotox- 

 icity consisted of dark-colored surface lesions about 1 cm 

 in diameter, apparently formed when soap concentrated at 

 the bottom of treated fruit. This injury might be avoided 



by the use of spreading agents to reduce soap accumula- 

 tion, by use of a different rate, or by spraying when drying 

 conditions arc optimal. 



We compared the cost of applying amitraz and 

 Safer soap using a price of $45 per gallon for amitraz and 

 $9 per gallon for Safer soap (retail price when purchased 

 in volume) and recommended rates. The use of Safer soap 

 ($54 per acre using a 3(X) gal. dilute base) was 37% more 

 costly than amitraz ($34 per acre) under the conditions of 

 our test. However, the manufacturer reports that they arc 

 working on a second-generation material which is hoped 

 will be as effective as the present soap but at 30% to 50% 

 of the cost. Moreover, it is difficult to estimate the value of 

 reduced pesticide resistance, reduced outbreaks of secon- 

 dary pests (e.g., mites), and of reduced negative effects on 

 beneficial species that may result from the use of soaps. 

 Also unknown at this time is whether or not growers could 

 receive a premium price in specialty markets by growing 

 "low-spray" or even "organic" pears using dormant oils 

 and soap sprays as the basis of a spray program. Positive 

 results in these areas could easily affect the economics of 

 spray decision-making. 



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