Identifying Secondary and Micronutrient Deficiencies:
Dr. Don C. Wilkerson, Professor and Extension Specialist
Department of Horticultural Sciences
Texas A&M University
College Station, TX
The correct diagnosis of micronutrient deficiencies is important in maintaining optimum plant growth. The recognition of these symptoms allows growers to "fine tune" their nutritional regime as well as minimize stress conditions. However, the symptoms expressed are often dependent on the species of plant grown, stage of growth or other controlling factors. Therefore, growers should become familiar with nutritional deficiencies on a crop- by-crop basis.
Because plant symptoms can be very subjective it is important to approach diagnosis carefully. The following is a general guideline to follow in recognizing the response to nutrient deficiencies:
Calcium (Ca) - From slight chlorosis to brown or black scorching of new leaf tips and die-back of growing points. The scorched and die-back portion of tissue is very slow to dry so that it does not crumble easily. Boron deficiency also causes scorching of new leaf tips and die-back of growing points, but calcium deficiency does not promote the growth of lateral shoots and short internodes as does boron deficiency.
Magnesium (Mg) - Interveinal chlorotic mottling or marbling of the older leaves which proceeds toward the younger leaves as the deficiency becomes more severe. The chlorotic interveinal yellow patches usually occur toward the center of the leaf with the margins being the last to turn yellow. In some crops, the interveinal yellow patches are followed by necrotic spots or patches and marginal scorching of the leaves.
Sulfur (S) - Resembles nitrogen deficiency in that older leaves become yellowish green and the stems become thin, hard, and woody. Some plants show colorful orange and red tints rather than yellowing. The stems, although hard and woody, increase in length but not in diameter.
Iron (Fe) - Starts with interveinal chlorotic mottling of immature leaves and in severe cases the new leaves become completely lacking in chlorophyll but with little or no necrotic spots. The chlorotic mottling on immature leaves may start first near the bases of the leaflets so that in effect the middle of the leaf appears to have a yellow streak.
Manganese (Mn) - Starts with interveinal chlorotic mottling of immature leaves and, in many plants, it is indistinguishable from that of iron. On fruiting plants, the blossom buds often do not fully develop and turn yellow or abort. As the deficiency becomes more severe, the new growth becomes completely yellow but, in contrast to iron necrotic spots, usually appear in the interveinal tissue.
Zinc (Zn) - In some plants, the interveinal chlorotic mottling first appears on the older leaves and in others, it appears on the immature leaves. It eventually affects the growing points of all plants. The interveinal chlorotic mottling may be the same as that for iron and manganese except for the development of exceptionally small leaves. When zinc deficiency onset is sudden such as the zinc left out of the nutrient solution, the chlorosis can appear identical to that of iron and manganese without the little leaf.
Boron (B) - From slight chlorosis to brown or black scorching of new leaf tips and die-back of the growing points similar to calcium deficiency. Also the brown and black die-back tissue is very slow to dry so that it can not be crumbled easily. Both the pith and epidermis of stems may be affected as exhibited by hollow stems to roughened and cracked stems.
Copper (Cu) - Leaves at top of the plant wilt easily followed by chlorotic and necrotic areas in the leaves. Leaves on top half of plant may show unusual puckering with veinal chlorosis. Absence of a knot on the leaf where the petiole joins the main stem of the plant beginning about 10 or more leaves below the growing point.
Molybdenum (Mo) - Older leaves show interveinal chlorotic blotches, become cupped and thickened. Chlorosis continues upward to younger leaves as deficiency progresses.
The diagnosis of nutrient deficiencies can be a key to optimizing plant growth. However, this technique is very subjective and requires careful observation. Plants respond to nutrient deficient conditions in several different ways. Growers must become familiar with these on a crop-by-crop basis.
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