P&PDL Picture of the Week for
June 15, 2009

Micronutrient deficiencies in red maple

Mike Mickelbart, Assistant Professor, Horticulture & Landscape Architecture, Purdue University

Plants require 16 essential nutrients to grow, flower, and set seed. Some of these nutrients (such as nitrogen, phosphorus, and potassium) are classified as “macronutrients”, whereas others are classified as “micronutrients.” The terms macro and micro refer to the relative abundance in the plant. However, all of these essential nutrients are important, so if one is missing (macro or micro), plant growth will be affected.

Micronutrients are often most available to plants at low pH (below 7). Some plants, such as red maple, are particularly sensitive to high pH soils. These plants exhibit micronutrient deficiencies when soil pH is high. The red maples in these pictures are showing classic micronutrient symptoms. The nutrient that is deficient in the leaf tissue is most likely iron, although manganese may also be limiting and it is impossible to diagnose properly without a plant tissue analysis.

The reason for this deficiency is that the irrigation water has a high pH. This will raise the soil pH, making micronutrients such as iron and manganese unavailable. This problem is exacerbated by the small soil volume. Soil or soilless media can act as a buffer against shifts in pH, but when the soil volume is small, there is less buffering capacity. The water used to irrigate these plants should be acidified to reduce the soil pH.

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Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service