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IS CHEMICAL PEACH THINNING ON THE HORIZON? 



Wes 1 ey R. Aut io 

 Department of Plant & Soil Sciences 

 University of Massachusetts 



To obtain fruit of adequate size and quality peaches must be thinned. 

 Presently, most thinning is done by hand or by knocking fruit off with 

 sticks, rubber hoses, or bats. Because of the labor intensive nature of 

 this operation much research has been devoted to finding chemicals which 

 when sprayed on the tree can thin peach fruit. Several compounds have been 

 tested and found to have undesirable properties, but recent work in Virginia 

 has given some promising results. 



A study in I98A by Byers, et al. (1) showed that reduction of photo- 

 synthesis of peach trees approximately at the time of "June drop" thinned 

 young fruit. They, first of all, showed this effect with simple shading, 

 but they also demonstrated a similar effect with a photosyn thes i s- i nh i b i t i ng 

 chemical, terbacil (Sinbar^). A second study (2) compared several other 

 photosynthes i s- i nhi b i t i ng chemicals and found that terbacil was the only one 

 which had potential as a peach fruit thinner. 



The results of the second study (2) showing the effect of terbacil on 

 peach trees is presented in Table 1. These were 20- to 25-year-old 

 'Madison' trees, and treatments were applied about 1 month after bloom. The 

 1000 ppm terbacil treatment removed about 1S% of the fruit and resulted in 



Table 1. The effect of terbacil treatments on peach thinning (from 2). 



Number of fruit per limb Fruit size 

 Treatment Pretreatment Post treatment at harvest 



Untreated 95 a^ 76 a 2.03 c 



Hand-thinned 2.21 a 



1000 ppm terbacil 86 a 23 b 2.21 a 



2000 ppm terbacil 68 a 16 b l.\k b 



^Means within a column not followed by the same letter are significantly 

 different at the 5% level. 



fruit of comparable size to the hand-thinned treatment. These treatments 



did not damage fruit, but some leaf damage did occur. The authors indicated 



that the levels used in this study were too high, and less than 500 ppm ter- 

 bacil likely would be effective. 



