the pink stage of flower development all blossom 

 clusters were counted on the two tagged limbs. 

 Blossom cluster density was calculated using LCA. 

 Trees were replicated based upon blossom cluster 

 density. All thmnmg treatments were applied with an 

 airblast sprayer calibrated to apply 125 gallons of 

 dilute spray per acre. Blossom thinner treatments were 

 applied May 4, 1998. Full bloom occurred about 0.5 

 day before application. Weather at the time of 

 application was partly sunny and warm with 

 temperature reaching 70°F soon after application. 

 Blossom thinning treatments were: 



ATS, Wilthin, and endothall thinned significantly and 

 comparably (Table 2). NAA did not thin when applied 

 as a bloom thinner. NAA at 6 ppm did not thin when 

 applied alone at the traditional postbloom timing or 

 when applied following any of the blossom thinner 

 treatments. All blossom thinning treatments increased 

 fruit size. NAA, when applied as a bloom thinner, 

 increased fruit size even though it did not significantly 

 reduce crop load. Likewise, the postbloom 6 ppm 

 application of NAA alone increased fruit size although 

 crop load was not significantly reduced. There were 

 no blossom thinner X NAA interactions. 



1 . Untreated control 



2. Ammonium thiosulfate (National Chelating) 6 

 gallons/acre 



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



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



5. NAA 12 ppm 



For plots that received post -bloom thinner, 6 ppm 

 NAA was applied on May 18, 1998 when fruit size 

 averaged 9.0 mm. Weather at the time of application 

 was sunny, warm and breezy with temperature at 76 to 

 78°F at application time and a high temperature of 80° 

 F was reached later in the day. 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 seven replications. 



Fruit set was evaluated by first counting all 

 persisting fruit on the tagged limbs at the end of June 

 drop in July. The fruit set was calculated by dividing 

 the number of fruit by the LCA. At the normal harvest 

 time on September 10, 40 fruit from each tree were 

 harvested randomly from around the periphery of the 

 tree. The harvested fruit were then taken to the lab 

 where total weight was taken and the average fruit size 

 calculated. Observation of the harvested fruit 

 indicated that there appeared to be no russet attributed 

 to treatment. 



Results 



Soon after application phytotoxic effects were 

 observed on the flower petals and leaves of all 

 blossom-thinned trees except those receiving NAA. 



Discussion 



ATS, Wilthin, and endothall were used in previous 

 years on apples at rates of 1 %, 6 qts/acre and 1 .5 pints/ 

 100 gallons, respectively, with disappointing results. 

 Little phytotoxicity was noted and minimal thinning 

 recorded. Higher rates were used this year in an 

 attempt to locate a rate where some thinning would be 

 achieved. Cool, damp, rainy weather immediately 

 preceded the application of blossom thinners in 

 Massachusetts. We speculate that the large amount of 

 phytotoxicity was attributed to greater penetration of 

 the thinner into the leaves because of the cool, cloudy, 

 and rainy weather the week before application rather 

 than due to an excessively high amounts of thinner. 

 While we have noted for years that absorption 

 following a cool wet penod can be increased, this may 

 be even more important when the thinner of choice, 

 thins by burning. 



It IS also interesting to note that fruit size was 

 increased significantly even though crop load was not 

 reduced significantly. Crop load may have been 

 reduced enough to increase fruit size. It is also 

 interesting to note that early thinning at bloom time 

 may actually increase fruit size more than by thinning 

 later. Note fruit size on trees treated with post bloom 

 NAA as compared with NAA used as a blossom 

 thinner. 



These data suggest that blossom thinning is a 

 viable and eftective way to reduce crop load. More 

 study is necessary to select the best chemical and 

 concentration to achieve appropriate thinning. 



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12 



Fruit Notes, Volume 67, Spring, 2002 



