The first visual symptom of copper (Cu) deficiency in wheat is a general wilting of the whole plant occuring at early tillering, even though the soil may be at field capacity. If the deficiency is severe enough, an effect on the development of tillering itself can be measured. Although there is initially a decrease in tillering as in other deficiencies, there may be a proliferation of tillers in severely Cu-deficient plants that occurs when Cu-adequate plants are experiencing stem elongation. Plants also appear lighter in color where Cu is deficient. These symptoms are generally only noticeable when comparisons are made with Cu-adequate plants.
Withertip, the first characteristic symptom of Cu deficiency, appears on young leaves. It shows as a sudden dying and withering (curling) of the tip end of the leaf blade, sometimes up to half the length of the blade. The base end of the leaf, however, can remain green until normal senescense occurs.
Under severe defieicny, as with calcium deficiency, the new growth can wither before unfolding and few heads will emerge. With less severe deficiency, heads may emerge but grains may not form in the spikelets at the tip of the head. The whole head takes on the appearance of a 'rat tail' with full grain in the base of the head, shrivelled grains in the middle of the head, and a withered necrotic tip. This rat tail appearance is sometimes confused with frost damage.
Marginal Cu deficiency may decrease grain yield by producing shrivelled grain and a bending over of the stem and head. Cu is required for the lignification of cell walls and hence a deficiency decreases stem strength.
Cu deficiency, can, along with some other factors, be responsible for the formation of the pigment melanin, resulting in a purpling of the stem, nodes, and even the spikelets glumes in some crops. Symptoms of Cu deficiency in the field may be many and varied. Symptoms on vegetative growth range from a paleness and floppiness of leaves to withertip. In many cases, effects do not show up until heading or even later with a discoloration (melanin) of the stubble during and following harvest. Whole fields may be affected evenly when Cu is inherently low, but patches may also be seen.
