Analysis and Treatment of Chlorotic Quercus Spp. at Saint John's University in Central Minnesota.

Since 2010, many oak (Quercus spp.) (Quercus alba, Quercus bicolor, and Quercus rubra) trees on the campus of Saint John's University have shown signs of stress and subsequently died within a year or two. Stress has been observed most notably in the appearance of interveinal chlorosis, commonly associated with a soil micronutrient deficiency such as iron (Fe) or manganese (Mn). One challenge of growing oak trees on the Saint John’s University (SJU) campus is the relatively high soil pH. Oak trees prefer soil pH ranging from 5 to 6.5, yet soils around the SJU campus often have pH >7, which limits availability of several nutrients, including both Fe and Mn. The objective of this study was to inventory the oak trees on campus, evaluate their health status, and determine the potential causes of stress. In 2015, oak trees within the study area were inventoried and categorized based on their visual health status (presence of chlorotic leaves and/or epicormic branching). Soil samples and leaf tissue samples were collected from a subset of both healthy and stressed trees for analysis. Soil samples were analyzed for pH and a suite of macro- and micronutrients (N, P, K, Ca, Mg, Fe, Mn, Zn, Cu, and B). Leaf tissue samples were also analyzed for concentrations of the same suite of macro- and micronutrients. These results will identify any potential soil nutrient deficiencies and guide treatment decisions. This study will identify solutions to address the loss of these oak trees and minimize future economic costs of tree replacement while preserving the aesthetics of the SJU campus.