Eastern White Pine Iron Deficiency

Eastern White Pine yellows is manifested by a general light green or yellow cast to the foliage, shorter needles, and reduced growth of branches. Growth of white pines seems most affected when trees are located in poorly drained, alkaline soil regions.

A research program was initiated at The Ohio State University in 1974 to determine if the limiting factor in the growth of Eastern White Pine (Pinus strobus) was pH-induced iron chlorosis. Knowing that high pH was detrimental to a number of trees including many Oaks, a number of trees were treated with an iron compounds. The pH of the clay-loam soil in the area of the trees ranged from 6.9 to 7.4.

Capsules, marketed as Iron Medicaps and containing ferric ammonium citrate, were implanted in a spiral pattern into the trunks of the pines during the last week of March in 1974 and 1975. All trees were between 5 and 8 inches in diamter, measured 1 foot from the soil line, and received between three to six capsules/tree. Although pine resin exuded from the implantation sites, all the ½-inch wounds healed completely by the following September.

Periodic examinations of the treated trees during both years indicated a positive response to the iron implantations. Vegetative growth of treated pines was improved, needle length increased, and curling of needles was no longer evident. The most dramatic difference, however, was in the change in overall tree foliage color from a yellow-green to a more normal medium green as noted in Table 1. Laboratory studies have indicated that both the foliage iron level and total chlorophyll content were increased in treated trees.

These findings suggest that Eastern White Pines may become yellow or light green due to iron deficiency caused by alkaline soils. Since changing the pH of soils under landscape trees is somewhat difficult, if not impossible, supplying iron to the trees is a logical control measure. Previous work by the authors with ferric ammonium citrate capsules in Oaks has indicated that visual effects can be noted for 3 or more years from the initial application. The improved foliage color of white pines treated in 1974 was markedly visible as of July 1976 indicating a similar pattern.

Not all yellow or chlorotic trees should be treated with iron compounds as injury may occur. However, in most instances, chlorotic oaks and yellow Eastern White Pines will respond to iron treatments. A foliar analysis and soil test are recommended for verification of the nutrient condition of plant materials.

• © 1977, International Society of Arboriculture. All rights reserved.