Litchi tomato as a fumigation alternative in Washington state wine grape vineyards

Abstract

Context and purpose of the study – The northern root-knot nematode (Meloidogyne hapla) is one of the most prevalent plant-parasitic nematodes affecting Washington State Vitis vinifera vineyards. This nematode induces small galls on roots, restricting water and nutrient uptake. In new vineyards this can impede establishment. In existing vineyards, it can exacerbate decline in chronically stressed vines. While preplant fumigation is a common strategy for M. hapla management, its efficacy is temporary and relies on broad-spectrum chemicals that undergo frequent regulatory scrutiny. The trap crop litchi tomato (Solanum sisymbriifolium) showed promise in reducing plant-parasitic nematode densities in potato. This prompted field greenhouse experiments to evaluate its potential to reduce M. hapla in V. vinifera.

Material and methods – A field experiment was conducted in a commercial vineyard block with vines recently removed in Mattawa, WA, USA. Ground cover treatments consisted of plots: 1) seeded to litchi tomato for one year; 2) seeded to litchi tomato for two consecutive years; or 3) a weedy fallow control, all replicated 4 times in a randomized complete block design. Plots were watered with overhead irrigation and soil samples were collected in spring and fall. In a separate greenhouse experiment, 6-week-old litchi tomato and a ‘Roma’ tomato control were transplanted into 4-inch pots, inoculated with 500 M. hapla eggs per pot, and allowed to grow to specific development stages before destructively harvesting at two-week intervals to evaluate the duration of root development on M. hapla densities in the soil.

Results – In the field experiment, after one season of growth, litchi tomato reduced M. hapla densities by 74.5% relative to the weedy fallow. This significant effect was also seen the following spring with a 65.3% reduction.  By the end of the second season of growth, plots that were planted to litchi tomato for two years had an 83.1% reduction in M. hapla compared to weedy fallow plots. Soil samples collected in the spring after the second season has reduced levels (76.6%) of M. hapla in plots that were seeded for two years relative to control plots. This field experiment demonstrates that litchi tomato reduced M. hapla densities relative to allowing a site stay as a weedy fallow. Greenhouse trials are currently underway investigating how long litchi tomato needs to grow to be the most effective. Used in conjunction with M. hapla resistant or tolerant rootstocks and other post-plant nematicidal or nematistatic cover crops, our results demonstrate that litchi tomato has potential as part of an integrated pest management approach in the management of M. hapla in Washington State wine grape vineyards.