Population Dynamics of Mesocriconema xenoplax Parasitizing Sweet Cherry Trees in British Columbia, Canada

The ring nematode, Mesocriconema xenoplax, has become recognized as a widespread pest of sweet cherry trees in the Okanagan Valley of British Columbia (BC). Understanding the cumulative impacts of M. xenoplax on tree health, interpreting diagnostic sample data, and predicting the impacts of climate change on M. xenoplax population densities all depend on knowledge of the temporal dynamics of M. xenoplax populations and their linkage with soil temperature and moisture regimes. The objective of this study was to measure population densities of M. xenoplax on a monthly basis over five years, in relation to soil temperature and moisture regimes, in a 16-year-old irrigated sweet cherry orchard. We tested the following hypotheses: (i) population densities would start low each spring and increase continuously with soil degree-day heat accumulation during each growing season, and (ii) year-to-year variation in population growth during the growing season would be correlated with year-to-year variation in soil degree-day heat accumulation. The data did not support these hypotheses and indicated that although there were significant differences in population densities among sample dates, there were no regular seasonal cycles of population growth and decline. We suggest that in mature cherry orchards, density-dependent processes mask the influences of annual changes in soil temperature and moisture on population processes. The data indicate that for diagnostic sampling purposes, all seasons would be equally representative of M. xenoplax population densities in irrigated orchards in BC. Furthermore, the lack of any strong linkage between soil temperature regimes and within- or across-year population dynamics indicate that modeling efforts based solely on abiotic drivers of temperature and moisture would not likely represent changes in population dynamics of M. xenoplax that will actually occur with climate change.