Thinning IVIclntosli Apple Trees Witli 

 Blossom Thinners, With and Without 

 Post-bloom NAA: A Report to the New 

 England Tree Fruit Growers Research 

 Committee 



James R. Schupp 



Hudson Valley Laboratory, Cornell University 



Duane W. Greene 



Department of Plant and Soil Sciences, University of Massachusetts 



The objective of these studies was to test the 

 efficacy of blossom thinners to replace carbaryl for 

 obtaining selective thinning of Mchitosh apples. 



Evaluation in Maine 

 Materials & Method 



Mature Rogers Mclntosh/M.7 apple trees growing 

 at Highmoor Farm, Monmouth, ME were selected for 

 uniform bloom. Treatment plots were surrounded on 

 all sides by one or more buffer trees, to prevent over- 

 spray. All thinning treatments were applied with an 

 airblast sprayer calibrated to apply 135 gallons of 

 dilute spray per acre, with 70% of the spray delivered 

 to the top half of the tree canopy. Blossom thinning 

 treatments were applied May 1 2, 1 998 when 70 to 80% 

 of the blossoms were open. The weather at the time of 

 application was sunny, temperatures was 72° F, with a 

 4 to 6 mph wind from the west. Blossom thinning 

 treatments were: 



1 . Untreated control 



2. Ammonium thiosulfate (National Chelating), 5 

 gallons per acre 



3. Wilthin (Entek Corp.), 12 quarts per acre 



4. Endothall (Elf Atochem), 2 pints per 100 gallons 



5. NAA, 12.5 ppm 



For plots that received post-bloom thinner, six 

 ppm NAA was applied on May 27,1 998 when fruitlet 

 diameter was 10 mm. The weather at the time of 

 application was sunny, temperature 64° F, with a 1 to 2 

 mph west wind. The treatments were arranged as a 

 split plot design. Blossom thinners were the main plot 

 treatment, postbloom NAA was the sub-plot 

 treatment, and there were five replications. 



Fruit set was evaluated by limb counts and by 

 cluster counts. All the flower clusters on one or two 

 limbs per tree were counted at pink. The limb 

 circumference was measured, and limb cross-sectional 

 area (LCA) was calculated. The number of fruit on 

 each limb was counted, and fruit set was calculated as 

 the number of fruit per 100 clusters and as the number 

 of fruit per LCA. Fruit counts were done shortly after 

 petal fall and again in July to evaluate both initial and 

 final set. Twenty-five fiower clusters on each tree 

 were tagged, and the number of fiowers on each cluster 

 was recorded. The number of fruit on each cluster was 

 counted and fruit set was calculated as the ratio of fruit 

 to flowers for each cluster. 



Yield per tree was determined in a single picking 



The Maine portion of this study was conducted at the University of Maine Highmoor Farm, during the time that Dr 

 Schupp was with the University of Maine. 



Fruit Notes, Volume 67, Spring, 2002 



