Effect of cultural practices and fungicide treatments on plant vigor and mortality of blueberries grown in Phytophthora infested soil

Phytophthora root rot is an important disease of blueberries, especially those grown in areas with poor drainage. Reliable cultural and chemical management strategies are needed for control of this disease. Three studies were conducted to evaluate the effects of cultural practices and fungicide treatments on plant vigor and mortality of blueberries planted in Phytophthora cinnamomi infested soils. One-year-old 'Star' and two-year-old 'Legacy' blueberry plants were transplanted to flat or raised beds (whole plots) fertilized with 0.5×, 1×, or 2× levels of nitrogen as urea (subplots). Within subplot treatments were soil amendments (pine bark, peat, none), fungicide treatments (phosphorous acid foliar, fosetyl-Al foliar and drench, and mefenoxam drench), or a combination of fungicide (mefenoxam) and soil amendment (peat). Plant vigor was rated twice a year. 'Star' plants were grown for five years and 'Legacy' plants were grown for two years. At the conclusion of each study plants were harvested and their top and root dry weights were recorded. At each bi-yearly evaluation, 'Star' plants grown on raised beds were more vigorous than those grown on flat beds; however, there were no significant differences in overall plant vigor or mortality due to nitrogen level. 'Star' plants in the phosphorous acid treatment consistently received high plant vigor ratings. After two years, 'Legacy' plants fertilized with the 2× nitrogen level had the highest vigor score, the greatest percentage of living plants, and the greatest top dry weight; and plants in the fosetyl-Al foliar, phosphorous acid, and mefenoxam treatments received higher vigor scores and had greater top weights than plants in the control treatment. There were no significant differences in vigor scores, percentage living plants, and top weights of plants due to soil amendment treatments.