Issue: April 19, 2003

Iron chlorosis treatment

Question:

Every year I have a problem with yellow leaves and dead twigs on my fruit trees. I was told this is iron chlorosis and that I needed to treat the trees with iron. I did that last summer, but the leaves stayed yellow. What can I do to solve this problem?

Answer:

Iron chlorosis is observed in many introduced plants that are grown in New Mexico. Even some native plants moved from mountainous regions to the mesas and valleys will exhibit chlorosis. This chlorosis is expressed as a yellowing of the leaf tissue between the veins that remain green. In severe cases of chlorosis, browning and death of the leaves and twigs may be observed. According to Dr. Robert Flynn, NMSU Extension Service Agronomist, the cause of chlorosis can be related to iron, zinc or other micronutrient deficiencies. The most common deficiency is iron caused by high pH soils (alkaline) and/or the presence of lime. Soil testing may reveal sufficient iron, but plants that are sensitive to alkaline soils or excess lime are not able to extract the iron for use in the plant. The solution to this problem is to supply iron to the plants in a readily available form. This may be done as foliar sprays or soil application of iron chelates or iron sulfate. Chelates (pronounced "key-lates") are organic (carbon-based) compounds that hold the iron, releasing them to the plant roots but preventing them from becoming bound to the soil and unavailable to plants. Dr. Flynn points out that all iron chelate products do not work equally well in New Mexico soils. He recommends iron chelates based on ethylenediamine di(o-hydrophenylacetic) acid (EDDHA), which are best at providing iron to plants in our high pH soils. The most common chelate, EDTA, is really meant for soils with a pH of less than 7 that are common in the eastern part of the U. S. Dr. Flynn recommends soil testing to determine the soil pH and help determine which chelate will be most effective for soil application in a specific garden or landscape. He says that most chelates should work well as foliar applications as long as label directions are followed. Iron sulfate can also be effective in New Mexico soils when applied at the right time. Foliar feeding needs to occur in the development phase of leaf tissue (spring). Time of day can also impact the efficiency of foliar feeding. Dr. Flynn noted that plants sensitive to chlorosis often need more than one feeding of iron each year. He suggests multiple applications during the growing season in order to keep these plants healthy..

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For more gardening information, visit the NMSU Extension Horticulture page: desertblooms@nmsu.edu.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505-865-7340, ext. 113.