28 CIRCULAR 867, U. S. DEPARTMENT OF AGRICULTURE 



where thinning operations were similarly performed, chemical thin- 

 ning (supplemented with hand thinning if necessary) has invariably 

 resulted in small but consistent increases in fruit size over conven- 

 tional hand thinning. During the past 6 years with 65 separate ex- 

 periments involving 2,600 trees the check (hand-thinned) trees aver- 

 aged 15 more fruits per box than chemically thinned trees. 



Results on fruit size have been variable in experiments where 

 naphthaleneacetic acid has been compared with the dinitro chemi- 

 cals. In New York (39) with several varieties of apples about the 

 same benefit in increased fruit size was obtained when the two types 

 of thinning agents were compared. In Washington naphthalene- 

 acetic acid generally has not produced so much larger fruits as might 

 be expected on the basis of the amount of thinning accomplished. 

 This probably is due to the fact that fruit generally attains con- 

 siderable size before dropping when naphthaleneacetic acid is used. 

 Experimental results in Washington indicate that unless the use of 

 naphthaleneacetic acid results in more thinning than is desirable 

 there is little or no benefit in fruit size as compared with hand- 

 thinned check trees. 



It is evident from the data presented in table 7 that fruit yields 

 were about the same when trees sprayed with Elgetol were compared 

 with either unthinned or hand-thinned check trees. As will be shown 

 later, chemical thinning sprays tend to increase yields over a period 

 of 2 years or more through their effect in altering the biennial bear- 

 ing habit of apple trees. It is of course obvious that if thinning 

 sprays are applied under conditions resulting in fruit-set reduction 

 below the limit of a capacity crop fruit yields will be adversely 

 affected. 



Biennial Bearing 



Heavy and light crop years with apples usually result from an 

 excess of fruit setting on the tree during the "on year." When the 

 quantity of fruit on the tree in relation to the amount of foliage is 

 excessive, fruit-bud formation is either reduced or may entirely fail 



Table 8. — The effect of Elgetol thinning sprays on yield and bearing 

 habit of apple trees over a period of several years in certain areas 



Variety 



Treatment 



Trees 



per 

 treat- 

 ment 



First 

 year 



Second 

 year 



Third 

 year 



Fourth 

 year 



Average 

 total 

 yield 



per tree 



State and 

 literature 

 reference 



Golden 

 Delicious. 



/Check *_ 

 \Elgetol__ 

 /Check * _ 

 \Elgetol- 

 /Check 2 _ 

 \Elgetol- 



Number 



10 

 10 

 10 

 10 

 10 

 10 



Boxes 



35 

 37 



41 

 52 

 20 

 17 



Boxes 



25 

 36 



9 

 23 





 12 



Boxes 



47 

 36 



Boxes 



6 

 30 



Boxes 



113 

 139 

 50 

 75 

 39 

 65 



> Washington. 



Beauty. 

 Wealthy 







ildaho U2). 



19 



15 







21 



\ New York 



/ (^)- 3 



1 Hand-thinned (35 to 50 days following bloom) if needed. 



2 Not hand-thinned. 



3 In the New York experiment a bushel was used as the unit of measure. 



