16 CIRCULAR 867, U. S. DEPARTMENT OF AGRICULTURE 



percent by the weaker concentration and 77 percent by the stronger 

 concentration. Naphthaleneacetamide at a concentration of 50 p. p. m. 

 used in a similar way reduced the number of spurs setting by 34 

 percent. Slight injury of the young foliage was caused by the 

 naphthaleneacetic acid at 10 p. p. m., while more severe injury in 

 the form of epinasty, scorching, and leaf drop resulted from the 

 stronger concentration of 50 p. p. m. No visible foliage injury fol- 

 lowed the naphthaleneacetamide spray. These results indicated that 

 naphthaleneacetamide was effective in reducing the set of Starking 

 but was less effective than naphthaleneacetic acid when used at the 

 same concentration. 



Schneider and Enzie (34), employing the branch-unit method, 

 found that bloom sprays of naphthaleneacetic acid at concentrations 

 of 100 to 300 p. p. m. seriously overthinned Delicious and Gano and 

 deformed the leaves. Similar results were obtained on Arkansas 

 Black with the same concentrations of naphthaleneacetic acid and 

 naphthaleneacetamide. The acid was more potent than the acetamide 

 in reducing set and causing leaf injury. 



In a second paper, Schneider and Enzie (35) reported that the 

 limbs of Delicious and Gano sprayed with these high concentrations 

 of naphthaleneacetic acid, which almost eliminated the crop, failed 

 to produce any more flowers the following year than untreated check 

 limbs, which had practically no bloom. Apparently this was due to 

 the dwarfing of leaves caused by the spray. In the case of the 

 Arkansas Black, which was a more annual blossoming variety under 

 their conditions, the percentage of flowering points in 1913 based 

 on the number of flowering points in 1942, the year of treatment, 

 was as follows : Naphthaleneacetic acid 100 p. p. m., 39 percent : 

 naphthaleneacetic acid 300 p. p. m., 12 percent; napthaleneacetamide 

 100 p. p. m., 73 percent; naphthaleneacetamide 300 p. p. m., 81 per- 

 cent; and check limbs, 67 percent. 



In another test on Arkansas Black (limb-unit method) these in- 

 vestigators employed sprays of naphthaleneacetic acid during the 

 bloom at weaker concentrations, ranging from 10 to 10 p. p. m. 

 These treatments resulted in less reduction in set than the stronger 

 concentrations, and the data indicate that the degree of thinning was 

 associated with concentration. Leaf injury was recorded as none to 

 slight, following the use of these concentrations. Naphthaleneacetic 

 acid at 40 p. p. m. reduced fruit set approximately twice as much 

 as naphthaleneacetamide at 80 p. p. m. concentration. The 40 p. p. m. 

 spray of naphthaleneacetic acid caused slight leaf injury, while the 

 80 p. p. m. of naphthaleneacetamide caused none. 



Other growth-regulating chemicals used in these tests, at a wide 

 range in concentrations, included indolebutyric acid, indoleacetic 

 acid, and indoleproprionic acid. None of these chemicals signifi- 

 cantly reduced the set of Stayman, nor did indoleacetic acid or 

 indolebutyric acid affect the set of Arkansas Black. 



In studying the effect of growth-regulating chemicals on the set 

 of the Starking apple (limb-unit method), Greene (16) used sprays 

 of naphthaleneacetic acid at concentrations of 10, 50, and 100 p. p. m. 

 in a 0.1 percent polyvinyl alcohol-water solution. The set of fruit 

 was reduced in all cases, with the greater reductions occurring at the 



