212 PLANT GROWTH SUBSTANCES 



Peaches and Apricots. — Peaches and apricots delayed in picking to 

 attain proper maturity for canning are subject to considerable drop in 

 certain areas. Hesse and Davey (21) found that the Stewart apricot re- 

 sponded to both NAA and its amide but that with Elberta peaches the 

 response was so slight as to hold no commercial advantage. Effective 

 sprays for peach drop control would be a boon to the canning-peach 

 industry. 



Effect of preharvest sprays on fruit maturity. — Space will not permit a 

 review of the work on the effect of growth substance sprays on fruit 

 maturity, but the problem is of such importance in fruit storage that at 

 least brief mention should be included here. It now seems quite certain 

 that growth substances can and do hasten maturity of apples and pears on 

 the tree and affect their subsequent storage life. The extent of this effect 

 depends on the compounds used and their concentration, as well as on 

 the length of delay in harvest made possible by their use. Citrus consti- 

 tutes a notable exception, perhaps unfortunately, for in this case a 

 hastening of maturity might have important advantages in marketing. 

 The results of Blondeau and Crane (9) in hastening the maturation of 

 CaHmyrna figs from a normal 120-day period to 60 days by sprays of 

 2,4,5-trichlorophenoxyacetic acid indicate that important advantages 

 in time of ripening might be gained with certain fruits. 



Some Factors Influencing Effectiveness 



Methods of application. — Dust applications, assuming equal effective- 

 ness, have advantages over spray applications on the basis of lower 

 labor costs and more rapid coverage, particularly important in case of 

 large acreages. Hoffman, Edgerton, and Van Doren (23,24) reported 

 that under favorable dusting conditions NAA incorporated in a talc 

 dust was equivalent in drop control of Mcintosh apples to roughly 

 the same quantity of the compound applied as a spray. Southwick 

 (39,40), on the other hand, using the same concentrations and the same 

 variety, did not find dusts to be equal to sprays. Unfavorable conditions 

 for dusting are more apt to occur than for spraying, and this may explain 

 the lack of complete agreement. In subsequent work Southwick's results 

 with dusts were more nearly the equal of sprays (41). Marth, Batjer, and 

 Moon (28) have also compared dusts with sprays, using Stayman Winesap 

 as the test variety, and reported comparable results. The uncertainty 



