Impact of Vineyard Fallow Practices on Reducing Meloidogyne hapla Population Densities

The northern root-knot nematode (Meloidogyne hapla) is a common plant-parasitic nematode in northern grape production regions. This nematode induces small galls on roots, which restricts water and nutrient uptake, resulting in poor vine establishment or exacerbated decline in stressed vines. A study was conducted to explore the impacts of site management practices on M. hapla population densities following removal of wine grape (Vitis vinifera) vineyards in Washington State. Soil was collected from 38 fields, M. hapla second-stage juvenile densities in soil were determined, and to assist in identifying M. hapla in potentially low-population density samples, an eight week-long tomato (Solanum lycopersicum) bioassay was conducted. Vineyard managers also provided information on site management techniques. Of the 20 total management techniques and combinations explored (e.g., fallow duration, cover crops, mowing, irrigation, herbicide applications), only one component resulted in lower M. hapla population densities: duration of vine-free period. A duration of at least one-year post vineyard removal showed a decline in M. hapla population densities in the sampled former vineyard sites. These results suggest that a fallow period could be useful as a non-chemical management tool for M. hapla in vineyard replant soils. However, consideration of additional site management factors such as weed management, soil series and amendments, interim crop planting, and irrigation or accumulated rainfall that may support M. hapla development is necessary.