APPARENT BORON TOXICITY 



William J. Lord, Dept. of Plant and Soil Science 



and 

 Bertram Gersten, Feed and Fertilizer Control Service 



An excess of boron may 

 therefore, growers are caut 

 ment. Since boron toxicity 

 from 1-year-old Mcintosh tr 



have a deleterious effect on fruit trees; 



ioned against over-application of this ele- 

 is not common, pictured here are leaves 



ees which show typical symptoms of boron tox- 

 icity. Leaf injury from an over- 

 application of boron is distinctive 

 in that a loss of green color occurs 

 along the midrib and larger lateral 

 veins, being first apparent at the 

 base of the leaf blade. In severe 

 cases, loss of chlorophyll is more 

 extensive than shown in the picture, 

 marginal leaf scorch develops, and 

 the leaves drop . 



Samples of "normal" appearing 

 leaves were obtained from a Massa- 

 achusetts orchard on July 30, 1965, 

 from: A) 5 trees showing slight 

 foliar injury; B) 2 trees with very 

 slight foliar injury; C) M- trees 

 showing no apparent injury, but 

 from the rows where the injury oc- 

 curred; and D) M- trees in a row ad- 

 jacent to the rows with affected 

 trees. Trees most severely injured 

 could not be sampled because of de- 

 foliation and/or because leaves 

 without the symptoms could not be 

 obtained. The average boron level 

 of the trees in group A was 97 ppm, 

 in group B, 83 ppm, in group C, 

 70 ppm and in group D, 50 ppm. 



Since foliar symptoms of boron toxicity are distinctive and the 

 limited data indicate an abnormally high boron level (3 0-50 ppm appears 

 to be common boron levels of apple trees) , we feel sure that an over- 

 application of boron had occurred. 



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