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Potassium (K): The desirable level of K in bearing apple trees ex- 

 pressed as percentage dry weight is 1.25-1.60. In 1972, 35% of the 

 'Mcintosh' leaves were below these levels whereas only 13% of those 

 from 'Delicious' trees were found to be low in K. Since this ele- 

 ment generally is not higher than the desirable level in apple 

 leaves, K may be needed annually. 



The requirements for K (expressed as K^O) based on potential 

 yields are as follows: (a) less than 15 buT 1.3 lbs/tree; (b) 1" 

 to 25 bu: 1.3-2.7 lbs/tree; (c) more than 25 bu: 2.7-4.3 lbs/tree. 

 The KpO requirements can be supplied by applying muriate of potash, 

 a "complete" fertilizer, or either Sul-Po Mag* or K-Mag*. The lat- 

 ter two fertilizers may be of value when both K and magnesium (Mg) 

 are low, since they are sources of both of these elements. High 

 levels of K can depress both Mg and Ca, particularly if the soil 

 supply of Mg and Ca is low. 



Magnesium (Mg): Low magnesium levels (less than 0.25%) were present 

 in 20% of the leaves sampled in 1972. The Mg requirements of trees 

 can best be met by maintaining an adequate dolomitic liming pro- 

 gram. Since it takes several years before lime is effective in 

 correcting Mg deficiency, Epsom salt sprays can be used to help 

 correct the condition. Apply 2 or 3 sprays at the rate of 15-20 

 lbs per 100 gallons of water at the time of calyx, first cover and 

 second cover sprays. To avoid possible incompatibilities, the Ep- 

 som salt sprays should not be combined with the regular pesticide 

 sprays . 



Boron (B): B was generally low in the leaf samples obtained in 

 1972. B can be supplied to apple trees either by foliar or soil 

 applications. Use the most economical and convenient method. 



Soil applications of B should be applied to orchards every 3 

 years. Borax is the common material used. The rates of applica- 

 tion per tree vary with age and size. Apply 0.25 lb of fertilizer 

 borate (20.2% B) or its equivalent to young trees, 0.5-0.75 lb to 

 medium age and size trees, and 0.75-1.00 lb to large or mature 

 trees. If the soil application of B is followed by a wet spring 

 and summer, it may be advisable to apply 2 foliar applications of 

 B the following year. 



Many growers rely on annual foliar applications of B. The 

 usual practice is to add Solubor* to the first 2 cover sprays. 

 Fertilizer grades of borax may contain grit and should not be used 

 in a sprayer. Mature trees should receive 4 lbs of Solubor* per 



*Trade Name 



