to 4 and 6 gallons per acre, and application was made 

 again under favorable thinning conditions. Based on 

 these results we believe that consistent and effective 

 thinning with ATS can be achieved if between 3 and 5 

 gallons per acre are applied in 1 00 gallons of water per 

 acrer. The highest rate of endothall used was 1 .5 pints 

 per 100 gallon in 1999, and that seemed to thin 

 appropriately. Wilthin was the weakest thinner used, 

 and even when applied at 8 quarts per acre, which is, in 

 general, higher than previously used, it was still a 

 modest thinner at best. 



The importance of blossom thinning at bloom to 

 maximize fruit size at harvest has been recognized for 

 many years. While thinning can be done if thinners are 

 applied anywhere from pink to full bloom, the greatest 

 response is when application is made near bloom. 

 Thinners act by interfering with ovule fertilization, 

 either by preventing successful pollination or by 

 disturbing pollen tube growth. Results from this 

 investigation suggest that timing of application may 

 influence the thinners response. The best thinning 

 results were obtained in 1999 when treatments were 

 applied when blossoms were 65 to 80% open rather 

 than closer to 1 00% which was the situation in the two 

 previous seasons. If flowers open over a several-day 

 period, especially under cool conditions, there may be 

 ample opportunity for pollination and significant 

 pollen tube growth of many flowers, before 

 applications are made at full bloom . 



It was observed that blossom thinners did not thin 

 uniformly on the tagged limbs. There were some areas 

 of the limb that set a less than optimal number of fruit, 

 thus fruit were spaced more than 6 inches apart, 

 whereas other areas were set heavier and require more 



hand thinning. The reduction in final set by ATS in 

 1999 documents that excessive thinning was done. 

 Some hand thinning was also required on these same 

 limbs indicating that there were also areas where fruit 

 were clustered. 



Successful blossom thinning treatments resulted 

 in a reduction in hand thinning of between 50% to 

 80%. This reduction following blossom thinner use 

 can translate into a significant labor savings. In 

 general, it required about one hour to hand thin a 

 control tree. At $7.50 per hour, the cost of hand 

 thinning these trees would be about $800 per acre. A 

 50% to 80% reduction in hand thinning would be a 

 savings of between $400 and $640 per acre. 



Some of the blossom thinning treatments reported 

 in this investigation resulted in a reduction m yield, as 

 expressed by number of fruit per limb cross-sectional 

 area. Fruit from these lower yielding trees may pay a 

 grower more money than higher yielding hand-thinned 

 control trees, because fruit on blossom thinned trees 

 were larger, and higher prices are paid for larger fruit. 

 There is little demand for a peach less than 2.5 inches. 



We believe that blossom thinning of peaches in 

 New England is a practice that can be reliably and very 

 profitably used by growers. Key components for 

 success include selection of the proper rate per acre of 

 thinner to apply, application of the spray to mature 

 plantings in 100 gallons per acre of water in an 

 accurately calibrated sprayer, and spray in appropriate 

 weather before most flowers are pollinated, generally 

 before full bloom. In our estimation endothall and 

 ATS hold the greatest commercial potential as 

 blossom thinners on peaches. 



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10 



Fruit Notes, Volume 64 (Number 4), Fall, 1999 



