-8- 



Heat stress symptoms on pear foliage (Figure 4) are sometimes confused with Mg 

 deficiency. Symptoms of heat stress (scorch) appear suddenly after a period of intense 

 heat. The scorch generally can be found on spur and terminal leaves of several or 

 more branches throughout the trees, the leaves being partially brown or black. There 

 is no progression of symptoms from the older to the most recently-formed leaves on 

 terminal shoots as with Mg deficiency. Frequently, the majority of injured leaves 

 drop as the growing season progresses. The Bosc variety may be more susceptible 

 to heat stress than other pear varieties commonly grown in New England. 



Potassium (K). Figure 5 shows leaf margin burn caused by K deficiency. This symptom 

 can be easily confused with the leaf margin burn from calcium chloride sprays and 

 sometimes confused with Mg deficiency. However, unlike leaf burn from calcium 

 chloride sprays, the scorch of leaf margins due to K deficiency progresses from the 

 older leaves to the younger leaves of current season shoots as the season advances. 

 The scorch may turn gray in color. Fraying and tattering of the leaves may occur 

 due to loss of the dead areas along their margins. When the deficiency is severe leaf 

 drop commencing with the older leaves of current season's terminal growth, is evident 

 in the latter part of the growing season. Nevertheless, leaf analysis is sometimes 

 necessary to confirm the problem is K and not calcium chloride burn. 



Figure 5. Potassium deficiency symptoms on apple leaves. 



Total K absorbed and the total dry matter produced is similar for fruiting and 

 non-fruiting trees but in heavy-cropping trees is translocated into the fruits. Thus, 

 the demand of a large crop for K is great and both the tree and fruit may be deficient 

 in this element. Leaf injury because of K deficiency can cause pre-harvest drop and 

 reduce fruit size. In contrast, light cropping trees are probably much higher in K than 

 is needed because of "luxury" uptake. 



K deficiency symptoms are apt to be more frequent in dry years because drought 

 conditions reduces uptake of elements. 



