Exanthema in Pears and Its Relation to Copper Deficiency

Abstract

Bartlett pear trees showed marked improvement following spraying with Bordeaux mixture, or after the introduction of soluble copper salts into the trunks of the trees, while similar treatments with Fe citrate, Mn chloride and Zn sulphate were without effect. Analysis of leaves and twigs showed a lower Cu content in diseased than in healthy trees from the same orchard, and considerably less than in those from localities free from the disease. The Cu content of apparently healthy leaves from diseased trees, however, did not vary significantly from that of diseased leaves of the same tree, this relation being very similar to that obtained in plants affected with chlorosis due to Fe deficiency. The authors conclude that while exanthema in pear trees is probably due to Cu deficiency, no evidence was available to prove that it is this deficiency per se, or merely an indirect influence, e.g., the action of Cu in neutralizing the effect of soil toxins absorbed by the plant.