Cover Crop Alternatives for Nematode Management in Washington Vineyards
Bernadette Gagnier,* Maria Mireles, Inga Zasada,
and Michelle Moyer
*Washington State University – IAREC, 24106 North Bunn Road,
Prosser, WA, 99350-8694 (bernadette.gagnier@wsu.edu)
The northern root-knot nematode (Meloidogyne hapla) is the main plant-parasitic nematode affecting Washington State Vitis vinifera vineyards. This nematode induces small galls on roots, restricting water and nutrient uptake. This can impede vineyard establishment or exacerbate decline in chronically-stressed vines. While preplant fumigation is a common strategy for M. hapla management, its efficacy is temporary. Preplant and post-plant cover crops are a potentially viable addition to an integrated management approach for nematodes. Two trials were established to evaluate cover crops to reduce M. hapla densities in vineyards. Litchi tomato (Solanum sisymbriifolium) was used as a preplant fumigation alternative. We found that after one growing season, litchi tomato reduced M. hapla densities by 75% (fall 2020; p < 0.0002). This effect continued in the following spring with a 65% reduction (spring 2021; p < 0.0002). Fall 2021 sampling showed that M. hapla populations densities were reduced by 84% (fall 2021; p = 0.014) in plots that were planted to litchi tomato for two years. We are also evaluating Dracula oilseed radish (Raphanus sativus var. oleiformis), White Dutch clover (Trifolium repens) and Pacific Gold mustard (Brassica juncea) for post-plant nematode suppression. After one year, plots planted with Dracula oilseed radish reduced M. hapla densities by 81% relative to the bare ground control (fall 2021; p = 0.048). M. hapla population densities trended lower in plots planted with White Dutch clover and Pacific Gold mustard compared to control plots; however, this difference was not statistically supported (p = 0.078). Soil samples will be taken again in spring 2022. Combined, our results demonstrate that pre- and post-plant cover crops may play an important role in M. hapla suppression in Washington winegrape vineyards.
Funding Support: Washington State Grape and Wine Research Program; USDA National Institute of Food and Agriculture, Hatch project 1016563.
