36 CIRCULAR 867, U. S. DEPARTMENT OF AGRICULTURE 



These hormone sprays resulted in a "flagged" appearance of the 

 foliage, which existed for about 3 to 4 weeks after the application. 

 The trees, however, assumed a normal appearance well in advance 

 of harvest, and the fruits matured with excellent size and quality. 

 Exploratory tests with concentrations stronger than 30 p. p. m. re- 

 sulted in considerable foliage yellowing and occasional killing of 

 terminal shoot tips. 



The thinning of peaches with naphthaleneacetic acid sprays has 

 not been investigated sufficiently to justify any suggestions for com- 

 mercial use. They were limited experiences recorded here merely indi- 

 cate that the possibilities should be explored on an experimental 

 scale. 



EFFECTIVENESS OF CHEMICAL THINNING SPRAYS 

 ON PEARS, APRICOTS, AND PLUMS 



Pears 



Under favorable conditions of weather and cross-pollination Bart- 

 lett pears in the Northwestern fruit districts tend to set too heavily 

 for satisfactory size and quality. Limited experiments (table 11) 

 with this variety indicate that it responds to dinitro thinning sprays 

 in about the same manner as apples. It may be seen from the data 

 presented in table 11 that most of the spray treatments appreciably 

 reduced fruit set. Within the limits tested, the higher concentrations 

 of Elgetol (1 quart per 100 gallons) reduced fruit set slightly but 

 more consistently than th eweaker dosages. In the Kane orchard, 

 sprays applied 2 days later than full bloom (early petal fall) re- 

 sulted in about the same amount of thinning as the full-bloom sprays. 



The 1948 results obtained in the Peterson, Nichols, and Muffley 

 orchards are of interest in that they emphasize the importance of 

 cross-pollination when considering chemical thinning, particularly 

 in a year when fruit set is restricted by unfavorable weather. In the 

 Peterson orchard the Bartlett was interplanted with the Anjou, 

 which is considered a good pollinizer for Bartlett. In the Nichols 

 and Muffley orchard, Anjou pollinizers were located a distance of 160 

 feet and 2,000 feet, respectively, from the experimental trees. In 

 these three orchards it may be noted that fruit set on unsprayed trees 

 closely paralleled the proximity of pollinizers. 



As stated previously, successful use of thinning sprays is predi- 

 cated on the assumption that fruit set will be in excess of the 

 amount necessary for an adequate crop. When fruit set is limited 

 by lack of cross-pollination and/or unfavorable weather, thinning 

 sprays will frequently result in greater set reduction than desired. 

 As far as is known the same factors relating to the use of dinitro 

 sprays on apples are applicable in the case of pears. At the present 

 time these sprays are in limited commercial use on Bartlett pears in 

 central Washington under conditions where a heavy fruit set may 

 be expected. 



