Evaluation of Accel® as a Chemical 

 Thinner and Suggestions for Use in 1 995 



Duane W. Greene and Wesley R. Autio 



Department of Plant & Soil Sciences, University of Massachusetts 



The chemical thinner Accel® was made available 

 for the first time in 1994. It is an altered Promalin® 

 formulation. Both products contain the same amount 

 of the active thinning ingredient benzyladenine (BA), 

 but Accel contains 1/10 the amount of the other com- 

 mon ingredient, gibberellins A^^.^. They are different 

 products and they cannot and should not be used inter- 

 changeably. 



Last year we outlined the responses one could ex- 

 pect from the use of Accel and made suggestions for 

 the use in 1994 [Fruit Notes 59(2): 18-20]. Much of 

 the information in that article still is appropriate. The 

 purpose of this article is to review 1994 research re- 

 sults and make revised suggestions for use in 1995. 



1993 Thinning Results on Mcintosh 



A block of Marshall Mclntosh/Mark were selected 

 at the Horticultural Research Center in Belchertown. 

 Accel at 20 g a.i./acre and NAA 3 ppm plus 1 lb Sevin 

 50WP/100gal were ap- 

 plied when fruit were 

 10.5 mm in diameter. 

 Temperature at and fol- 

 lowing application was 

 between 60" and 65"F. A 

 second application of 

 Accel at 20 g a.i./acre 

 was made at 16.2 mm 

 diameter to one group of 

 trees that previously re- 

 ceived Accel. Tempera- 

 ture at the time of appli- 

 cation was about 60"F. 

 Relative to the control, 

 no treatment caused fmit 

 thinning and no treat- 

 ment influenced fruit size 

 at harvest (Table 1). The 

 only treatment to in- 



crease return bloom in 1994 was Accel applied twice. 

 Weather during thinning time in 1 993 was cool and 

 windy. The lack of thinning was not surprising since 

 chemical thinners generally do not perform well when 

 the temperature is cool during and immediately follow- 

 ing application. Accel increases cell division and cell 

 number in apples. Thus it can increase fruit size inde- 

 pendently of its effects on thinning. In 1993, neither 

 one nor two applications influenced final fruit size. We 

 conclude that warm temperature is required for Accel 

 to increase fruit size as well as to stimulate fruit abscis- 

 sion. Return bloom in 1994 illustrates that Accel has 

 the ability to increase return bloom even if it does not 

 thin. 



1994 Thinning Results on Mcintosh 



Thinning treatments in 1994 were applied to 

 Marshall Mclntosh/Mark either at petal fall when the 

 temperature was in the low 70's or at the 10 mm stage 



Fruit Notes, Spring, 1995 



