Gaetan Chiasson1 and Kelvin Lynch2
Abstract: A trial to evaluate the affect of nitrogen and phosphorous fertilization on leaf disease severity was established in a commercial blueberry field in Northumberland county New Brunswick in 2003. Treatments include 30 or 50 kg/ha of nitrogen as a spring application in the pruning year in combination with 50 or 200 kg/ha of phosphorous with either 0 or 25 kg/ha of additional nitrogen at tip dieback. Leaf samples for tissue analysis were taken at tip dieback and again in early September. Leaf disease incidence, primarily due to powdery mildew was assessed on August 8 and September 19, 2003 (pruning year) and August 17, 2004 (cropping year). Data on plant height, degree of branching, number of fruit buds and yield were taken in 2004. On a weekly basis during the 2003 and 2004 seasons blueberry stems were collected to assess the development of powdery mildew. Leaf tissue phosphorous concentrations ranged from a low of 0.12 percent to a high of 0.16 percent and nitrogen to phosphorous ratios ranged from 9.75 to 16.28. No significant differences were found between the treatments for leaf disease severity and there was no apparent correlation between disease incidence and either leaf tissue phosphorous concentrations or the nitrogen to phosphorous ratio. Additional nitrogen at tip dieback induced late season growth and increased stem branching. Additional nitrogen at tip dieback in combination with low phosphorous increased the number of fruit buds. Powdery mildew infections were detected as early as June in both seasons and disease incidence increased rapidly during July.
1NB Department of Agriculture and Aquaculture, Regional Agri-Business Development, 1625 King Avenue, Bathurst, New Brunswick E2A 1S7
2NB Department of Agriculture and Aquaculture, Crop Development Branch, P. O. Box 6000, Fredericton, NB E3B 5H1