Boron Deficiency in Walnuts
If walnut plants are boron deficient, large, irregular, necrotic patches develop between the veins, particularly on the terminal leaflets. When boron deficiency is severe, the leaves are twisted and the veins are very prominent. Dieback from tips of the shoots results in very evident leafless branches. The nuts do not set properly and a marked reduction in yield can be expected. Walnut trees do not usually need boron supplemenation until they reach bearing age (12 years).
Photo courtesy of Dr. Patrick Brown, University of California-Davis