-6- 

 CHmilCAL THIMING OF APPLES 



Dinitro Materials ,^jpl.. thinnin'^ preccnts nowc prc;bl»jas« Varieties vary- 

 widely in their tendency to set heavily, bear regularly, and in their pollination 

 requirements. The amount of bloom, time of bloom, vigor and age of trees, pollina- 

 ting vfeather, type of polienizers in the block, bee activity, soil, and nutritional 

 conditions of the tree must be considered. The dinitro materials, Elgetol and the 

 powder DN No, 1, are the most suitable dinitro materials. They must be used at 

 blossom time, IVith the varieties Yellow Transparent, Duchess, Y^ealthy, Baldwin, 

 and Golden Delicious, these materials should be applied the first day of full bloom 

 of the spurs. Some varieties, particularly Wealthy and occasionally Baldwin, may 

 have a large number of flower buds laterally and terminally on the past season's 

 shoots which generally open two or three days later than the spur bloom. On such 

 varieties, a second application at half strength is often necessary. For varieties 

 like Delicious, Northern Spy and H, I, Greening, the dinitros should be applied the 

 second day of full bloom. These varieties apparently need more time for cross 

 pollination to take place. These three varieties, v/hen vigorous, fully grovm, and 

 adequately cross pollenized, may need thinning to obtain suitable fruit size and 

 overcome their tendency to alternate. Of the dinitro materials, DN No. 1 is begin- 

 ning to gain favor over the liquid DII's and the pov/der DN No, 2, since it appears to 

 thin as v/ell as the other dinitros but is less caustic and injurious to the foliage. 



Following is a suggested concentration schedule when using the dinitro . 

 materials, 



Dinitro Per 100 Gals . 



V ariety Timo of Application Liquid Powder 



Duchess 1st day full, bloom 1 1/2 to 2 pts. 3/4 to 1 lb. 



Yellow Transparent 1st day full bloom 1 l/2 to 2 pts, 3/4 to 1 lb, 



Vfealthy 1st day full bloom 2 pts. 1 lb» 



(possible 2nd application 

 for lateral I; terminal 



bloom) 1 pt. 1/2 lb, 



Baldwin 1st day full bloom 1 l/2 to 2 pts, 1 lb. 



Golden Delicious 1st day full bloom 1 pt. l/2 lb, 



Delicious 2nd day full bloom 1 pt, l/2 Ib^ 



Hormones During the last tvio years considerable interest has been shown in 

 chemical thinning with naphthalene-acetic acid and some of its derivatives. It has 

 been used successfully on Delicious, Baldv/in, Yi'ealthy, and Northern Spy applied at 

 calyx time. The commercial preparation about which most is known is "App-L-Set" 

 and the concentrations suggested are based on experiments with it alone. Other 

 commercial formulations may or may not thin to the same extent. This type of 

 material has the advantage over the dinitro materials in that accurate timing of the 

 spray is not as important. Also, it may be applied after the blossom period when 

 there is less chance of frost and the maximum amount of pollination and fertiliza- 

 tion has token place. This period of delay can be important and helpful in deciding 

 whether to do any chemical thinning in "sarly blooming seasons or when weather condi- 

 tions have not been ideal for pollination and fertilization up to the time of 

 full blocm. 



However, the hormone materials may be somewhat erratic in performance and cause 

 occasional txvisting of the "leaves. Also, it is not yet known whether trees of such 

 alternate bearing varieties as TJealthy will bear annual crops follov/ing its use. In 

 other v;ords, v/e have loss experimental evidence v/ith this material than we have 

 with the dinitros. 



