62 STATE POMOLOGICAL SOCIETY. 



Trees heavily fertilized with nitrogen are undoubtedly more 

 susceptible to certain diseases than are trees not so fertilized. 

 For instance, fire blight is known to be more virulent on trees 

 that are growing rapidly. We have found in our work with 

 peaches that we had more brown rot on a block of peach trees 

 fertilized with nitrogen alone than we found with any other 

 fertilizer treatment. (Incidentally I may remark that we picked 

 this year an average of about eight bushels of peaches per tree 

 from those nitrogen fed trees.) Stewart of Pennsylvania 

 reports that nitfate- fertilized trees were more resistant to a 

 certain leaf disease. 



There has probably been more controversy over the value of 

 potash in orchard fertilization than any other element of plant 

 food. Potash is closely correlated with starch production in the 

 plant, and with protein formation and accumulation. Many 

 virtues have been ascribed to potash, such as earliness in ripen- 

 ing, fruit bud formation, increased color, and curative or immu- 

 nizing effects upon certain diseases. In our experience with 

 peaches, potash does not appear to hasten the maturity of the 

 fruit to any extent and I anticipate that its effect upon apples 

 would be entirely negligible. Fruits heavily fertilized with 

 potash often have higher color; but this color is due not to the 

 direct effect of the potash upon color, but to the fact that the leaf 

 surface upon the tree may diminish and thus let in more sun- 

 light. Potash is not a cure for disease. Heavy potash applica- 

 tions may cause the tree to produce a denser wood, increase the 

 sap pressure in the cells and thus make it more difficult for 

 certain diseases to gain a foothold in the tissues of the plant. 

 It has been claimed that potash will tend to increase the sugar 

 content of fruits ; but this has not as yet been proven. When 

 potash is applied to a soil that is somewhat deficient in both 

 potash and nitrogen, its effect is to cause the foliage to assume a 

 deeper green color. After a season or two this effect wears off. 

 Yellowness of foliage in an orchard that is well cared for in 

 every way and whose moisture supply is good, may be due to 

 either lack of potash, lack of nitrogen, or both. There is a 

 current belief that potash fertilizers add to the keeping qualities 

 of fruit. There is some evidence to support this view, but it is 

 not as yet conclusive. It is likely that this effect of potash 

 would be more noticeable in peaches than in apples. 



