8 - 



color. Growers definitely are using less N on Mcintosh than in 

 the past because we need medium-sized, well-colored apples with long 

 storage life. Some growers have not omitted N in mature Mcintosh 

 blocks for 5 to 8 years with no apparent harmful effects. 



Young vigorous trees are troublesome when they start bearing 

 a crop because of excessively large, poorly colored fruit and poor 

 keepability of fruit in storage. The reduction or omission of N 

 is frequently essential. This procedure plus limb positioning 

 (spreading) is needed on vigorous young Delicious trees to encourage 

 bloom and fruit set. 



Apply sufficient N to keep bearing Delicious trees vigorous. 

 N levels of 2.2 - 2.41 in bearing Delicious trees areprobably sat- 

 isfactory because it is necessary to keep the tree vigorous in order 

 to produce large-sized fruits. Furthermore, obtaining sufficient red 

 color on the newer strains of Delicious is not a problem. 



The N requirement can be met by applying calcium nitrate, am- 

 monium nitrate or urea sources of fertilizer N or a "complete" fer- 

 tilizer. (Growers concerned about bitter pit and/or cork spot may 

 wish to rely on calcium nitrate as the source of N.) However, the 

 phosphorous (P) in the complete fertilizer is not needed in our 

 orchards. Therefore, purchase a prepared mix that contains no P 

 or purchase an N and a K fertilizer and mix them prior to applica- 

 tion or apply them separately. Some growers apply the K fertilizer 

 in the fall and the N fertilizer in the spring. 



Potassium (K) : The K requirements of apple trees with a large 

 crop are high because the fruit utilizes about 3 times as much K as 

 N. Since the quantity of K stored by the tree is extremely small, 

 it seems important to supply adequate K this spring on trees that 

 had heavy fruit set in 1977. 



The requirements of apple trees for K (expressed as K2O) based 

 on potential yields are as follows: (a) less than 15 bu : 1.3 lbs/ 

 tree; (b) 15 to 25 bu : 1.3-2.7 lbs/tree; and (c) more than 25 bu: 

 2.7-4.3 lbs/tree. It is necessary, however, to maintain a balance 

 among the essential nutrients for apple trees. For example, exces- 

 sive levels of K can reduce both leaf and fruit Ca. Therefore, we 

 strongly urge that you participate in our leaf analysis program to 

 more accurately determine the K needs of your apple trees^ 



Calcium (Ca) : Cork spot and bitter pit, which are visual 

 evidence of low Ca levels in apples, was more prevalent than usual 

 on Delicious during the 1977-78 storage season. 



The Delicious on the left in the following photograph shows 

 bitter pit and the one on the right has cork spot. Bitter pit is most 

 frequently associated with the calyx end of the apple and its severity 



