Pre-Harvest Fruit Drop 249 



Side Effects of Auxin Sprays 



A side effect of these treatments which has gladdened the hearts 

 of apple growers is the increase in coloring of the fruits following 

 auxin spray application. This increased coloring was observed by 

 Gardner et al (1940) in their original study of the control of fruit 

 drop. However the extensive use of naphthaleneacetic acid in the 

 1940's minimized the coloring effect, and only recently when the 

 chlorinated phenoxyalkyl acids have been used (2,4-D, 2,4,5-T, 2,4,5- 

 TP) have pronounced increases in color been obtained. More intense 

 red coloration permits the sale of the fruit as a fancier product and 

 at a higher price. The extent of color development is dependent upon 

 the time of application in relation to the time of picking. If the fruits 

 are picked within two weeks of the time of spray, color is not generally 

 intensified, but longer periods of time between spraying and picking 

 w ill result in greater color development in response to the auxin. 



The development of greater coloration in apples is primarily 

 useful for fruit which is to be sold without being stored, for encour- 

 agement of coloring and ripening by auxin application shortens the 

 storage life of the fruits. 



There are many confficting reports in the literature on the ques- 

 tion of whether auxin applied to prevent pre-harvest drop alters the 

 rijjening and storage performance of the apples. There is clear evi- 

 dence that auxin (auses an increase in the respiratory rate of the 

 fruits, and if this increased metabolic activity is permitted to continue 

 over a long period of time the fruits will necessarily ripen more 

 rapidly (Smock and Gross, 1947). The conflicting findings of many 

 different authors that auxins did or did not shorten the storage life 

 Avere finally clarified by Gerhardt and Allmendinger (1945), who 

 demonstrated that if the fruits were placed in storage within two 

 weeks of the time of spraying with naphthaleneacetic acid there was 

 no noticeable hastening of ripening or shortening of storage life. 

 However, if the frviits remained on the tree or out of storage for more 

 than two weeks from the time of auxin application, ripening was 

 hastened and the storage life definitely shortened. The same situa- 

 tion appears to exist following treatment with 2,4,5-TP (Southwick 

 et al, 1953). 



A promising means of preventing the early ripening due to 

 auxin treatments has been suggested by Smock et al (1951) who 

 show^ed that incorporation of maleic hydrazide into the auxin spray 

 effectively removed the stimulation of respiration by the auxin 



