EXANTHEMA IN PEAR, AND COPPER DEFICIENCY

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Abstract
Shoot tips of affected trees blacken and die in late spring. Young leaves burn at the edge with characteristic striations. Affected trees can be cured by application of Cu salts to the soil, by introducing crystals of Cu salts into the root crown of the tree or by spraying with Bordeaux mixture. MnCl2. ZnSO4, ferric citrate, K2Cr2(SO4)3, NaVO3, CdSO4, Co(NO3)2 and Ni(NO3)2 did not correct the disease, a fact which supports the contention that Cu salts exert a specific beneficial action. The copper content of leaves and shoots from healthy and diseased trees was detd. and compared. It was invariably lower in trees within the exanthema area than in trees in localities free of the disease. There was no consistent difference in the Cu content of healthy and diseased leaves from trees in the orchard where exanthema exists. Exanthema is evidently due to a deficiency of copper per se.