14 A[ASS. EXPKRUrKNT STATION HUIJ.KTIN 3S] 



adapted to sucli a setup. Past records of drop sliould enable growers to 

 choose the particular orchards that have caused the most trouble with 

 excessive fruit drop year in and year out. These should have precedence 

 in receiving hormone sprays over orchards whicii have a record of pro- 

 ducing fruit that attains good size, color, and maturity before falling to 

 the ground. 



Experiment with Excised Branches 



Two similar branches of a Mcintosh tree were chosen for a comparative 

 study of fruit drop following their removal from the tree. One was 

 sprayed thoroughly on September 18 with a hand pressure sprayer using 

 a spray containing 20 p. p.m. of naphthalene acetic acid. The other branch 

 served as a check. On September 22 the two branches were carefully 

 removed from the tree and the cut ends were placed in water. The 

 branches were supported so that their previous positions relative to the 

 horizontal were approximately maintained. There was some dropping 

 of apples within a few days from the unsprayed branch, and apples con- 

 tinued to absciss until all (23j had dropped. The hormone-treated branch, 

 however, showed practically no dropping of its 36 apples for longer than 

 two weeks. Even a month later, after two freezes, some apples were still 

 hanging. Previous work (6) has indicated that an injured limb may 

 exhibit delayed dropping of fruit to some degree and possibly these 

 branches so behaved. However, the effect from the spraying was far 

 more significant than the effect from the cutting itself. 



SUMMARY AND CONCLUSIONS 



'iiie use iii so-called hormone or drop-control spra\s to tlecrease the 

 preharvest dropping of apples offers some promise to fruit growers in 

 Massachusetts. The method is still in the development state and the 

 material in thi.s bulletin sums up much of the present knowledge concern- 

 ing it. Some aspects are more definitely established than others where 

 results have not been sufficiently extensive or uniform for positive con- 

 clusions. That certain chemicals, such as naphthalene acetic acid and 

 naphthalene acetamide, when dissolved and diluted in water and applied 

 to apple trees around harvest time, exert a retarding effect on natural 

 fruit drop is well authenticated. 



There is no doubt also that the effect of these and other chemicals is 

 variable. Many factors may contribute to this variability, such as variety, 

 time of application, thoroughness of application, concentration, weather 

 conditions, and season. These factors and other considerations iiave 

 been discussed and the attempt has been inade to evaluate their signif- 

 icance on the basis of exjjeriniental tests. Most of the work was done 

 with Mcintosh. 



The effective period of hormone spra\'s is tiie number of da\-s that a 

 retarding influence on drop is maintained and varies greatl\' with variet\ . 

 With MclntoNh and Wealthy this period was about 10 to 12 da.\s. With 

 other varieties, it is usually somewhat longer. 



The practical effect of a S];ray application is not immediately apparent. 

 L'sually from two to three da\'s elapse before dropping is measurably 



