Toxicity Symptoms

The visual symptoms of manganese toxicity vary depending on the plant species and the level of tolerance to an excess of this nutrient. Localized as well as high overall concentrations of manganese are responsible for toxicity symptoms such as leaf speckling in barley(112), internal bark necrosis in apple (113), and leaf marginal chlorosis in mustard (Brassica spp. L.) (114).

The symptoms observed include yellowing beginning at the leaf edge of older leaves, sometimes leading to an upward cupping (crinkle leaf in cotton, (115)), and brown necrotic peppering on older leaves. Other symptoms include leaf puckering in soybeans and snap bean (116); marginal chlorosis and necrosis of leaves in alfalfa, rape (Brassica napus L.), kale (Brassica oleracea var. acephala DC.), and lettuce (Lactuca sativa L.) (116); necrotic spots on leaves in barley, lettuce, and soybeans (116); and necrosis in apple bark (i.e., bark measles) (60). Symptoms in soybeans include chlorotic specks and leaf crinkling as a result of raised interveinal areas (117,118); chlorotic leaf tips, necrotic areas, and leaf distortion (102) in tobacco (Nicotiana tabacum L.).