CORVALLIS, OR Diseases caused by a species of fungus called Phytophthora syringae are responsible for significant economic losses on a wide range of plants, including pear. In the Pacific Northwest region of the United States, disease occurs during the winter in nursery stock, especially on trees that are harvested and stored in coolers or in outdoor sawdust beds. Recent field observations by growers suggest that increased nitrogen content in nursery trees resulting from foliar sprays with urea in the autumn increases tree susceptibility to infection by Phytophthora syringae. The results of new research suggest the relationship between tree susceptibility to P. syringae and tree nitrogen concentration may be specific to the form of nitrogen, delivery method, or timing of nitrogen applications.
Researchers from Oregon State University's Department of Horticulture and the USDA-Agricultural Research Service published a study in HortTechnology that contains new answers for nursery operators. The experiments investigated the effects of soil nitrogen (N) availability and spraying pear trees with combinations of urea, chelated copper ethylenediaminetetraacetic acid (CuEDTA), and phosphonate-containing fungicides on stem N concentration and susceptibility to infection by P. syringae.
Experimental results showed that spraying trees with urea in the autumn increased concentrations of nitrogen and amino acids in stems and had no significant effect on tree susceptibility when stems were inoculated with P. syringae before or after urea sprays. Spraying with CuEDTA decreased stem nitrogen concentrations and had no significant influence on tree susceptibility to P. syringae when stems were inoculated before or after CuEDTA sprays, while spraying with fungicides containing fosetyl-aluminum in October or November decreased tree susceptibility to P. syringae. The effects of fungicides containing fosetyl-a
|Contact: Michael W. Neff|
American Society for Horticultural Science