Rothamsted Symposium on Trace Elements 86 



1) on the leaves: 



a) a yellow mottling of the leaves sometimes according to a dis- 

 tinct pattern. 



I?) an undulation of the leaf margin. 



c) the leaf hecomes very narrow with a length of only one-third of 

 the normal length. 



2) on the shoots: 



a) shortening of the distance between the leaf insertions near the 

 end of the shoot, with a resetting eflFect. 



&) late ripening of the end of the shoot and delay in the forma- 

 tion of the terminal bud. 



c) insuflBcient formation of wood with the resiJt that the twigs re- 

 main weak and thin, as if there were some wood disease. 



d) outgrowth of many side branches near the end of the shoot in 

 the second year resulting in a witches' broom appearance. 



3) on the fruit, no special characteristics, but the fruits remain very 

 small. 



4) on the tree as a whole: 



an erratic spread of diseased branches amidst quite healthy parts of 

 the tree. 



5) throughout the year: 



in less severe cases one will notice the varying degree of severity of 

 s)nmptoms in the course of one season on one shoot. A shoot, 

 e.g., may start growing well, develop clear symptoms in early 

 summer, to show, in late summer, again a healthy top with green 

 leaves. 



In other apple varieties there is much less growth in cases of 

 zinc deficiency than we find in "Golden Delicious." The stunted 

 growth is more obvious and the eflFect of rosetting more marked. 



The disease results in very poor foliage at the end of a long, 

 weak branch. This indicates the rather sudden appearance of 

 zinc deficiency symptoms after years of normal growth. In Hol- 

 land we have seen these symptoms particularly on the variety 

 "Perzikrode Zomerappel" and also on such varieties as Keswick 

 Codlin, Cox, Glory of Holland, etc. 



Pears may be aflFected too. They show stunted growth, small 

 leaves and intervenal chlorosis. It has been proved that the dis- 

 ease occurs also on the cherry. 



There is little to be said at present regarding the soil conditions 

 causing this disease. There is no reason to assume that an excess 

 of phosphorus is the reason for the disease as observed in Den- 

 mark. It occurs mostly on light sandy soils, which are rather high 

 in lime content. 



In Holland, hitherto, the disease has only been noted in the 

 South on some islands of the province of Zeeland. 



