Phytotoxicity from incorrect iron chelate applications

Iron deficiencies are common in spring bedding plant production, and iron chelates are often applied to quickly green up crops. However, more selective applications followed by thorough foliage rinsing help prevent plant damage.

Christopher J. Currey of Iowa State University was asked to visit a grower who was experiencing problems in a double-poly film greenhouse filled with seasonal spring bedding plants. As soon as he entered the greenhouse, the damage was obvious. On some species, leaves were covered with necrotic spots and margins. On others, newer leaves showed cupping and curling. Some plants displayed both symptoms.

The two most common issues across species were necrotic foliage and cupping leaves. These symptoms are often associated with pesticide injury. The grower had been battling thrips and whiteflies, but the pesticide used and its concentration appeared appropriate and safe. As they continued discussing conditions in the greenhouse, he mentioned that he typically sees chlorosis on his petunias (Petunia spp.) and calibrachoa (Calibrachoa spp.), and this year he was trying to prevent it.

Interveinal chlorosis on petunias and calibrachoa is most often caused by a micronutrient deficiency, with iron (Fe) frequently the limiting nutrient. Iron deficiency can result from either: 1) adequate iron in the root zone that becomes less available due to elevated pH; or 2) insufficient iron in the root zone. While specific corrective measures depend on the underlying cause, one solution addresses both: applying an iron chelate. In this case, an iron chelate had indeed been applied.