Post-plant nematicide timing for northern root-knot nematode in Washington wine grapes

Abstract

Context and purpose of the study – Vigor declines in older vineyards and poor vine establishment in replant situations have been attributed to plant-parasitic nematodes. The northern root-knot nematode, Meloidogyne hapla, is the most prevalent plant-parasitic nematode species found in Washington wine grape vineyards. Management for nematodes in established vineyards is limited to the application of post-plant nematicides. We are evaluating new nematicides that are currently not registered in grape for their efficacy in controlling M. hapla and a part of that evaluation includes improving the alignment of nematicide application timing with the vulnerable second-stage juvenile (J2) life stage of M. hapla. Work done concurrently with this research found that M. hapla J2 are at their lowest density in midsummer, increase to a maximum density between October and March, then decline over spring and early summer (East et al., in press). The influence of product timing on its efficacy will be presented.

Materials and methods – Five vine plots in a Vitis vinifera ‘Riesling’ vineyard were soil sampled for M. hapla J2 in spring 2016 to establish baseline nematode densities. Nematicide treatments of fluazaindolizine (Salibro, total acre rate) and fluensulfone (Nimitz, treated acre rate) were applied according to manufacturer recommendations once in spring 2016; each treatment had four replicate plots. In spring 2017, an additional three spring Salibro treatments, calculated from treated acre rather than total acreage were added: full rate, half rate, and half rate applied twice; and a Nimitz treatment (half rate applied in spring and fall). In spring 2018, a second vineyard site planted to ‘Chardonnay’ was added, with Salibro treatments calculated from treated acre: full rate in spring, half rate in spring, full rate in fall, and half rate in spring and fall. Soil was sampled in each plot to measure M. hapla J2 densities in spring and fall from 2016 through 2018. Dormant pruning weights and whole vine yield were measured to assess effect of nematicide treatments on vine growth.

Results – The total acre rate of Salibro had lower densities of M. hapla J2 than the untreated control in fall 2016, 2017, and 2018 at the Riesling vineyard. Unfortunately, this is not a rate that will be legally registered. The half rate applied twice spring treatment was only effective starting fall of 2018, after two years of application. In fall 2018, both full rate in spring and half rate in spring treatments reduced J2 densities at the Chardonnay vineyard. No other Salibro or any of the Nimitz treatments reduced M. hapla J2 densities. Vine parameters were not affected by nematicide treatments. Spring 2019 results will be available at time of presentation, and we are particularly interested in the longer-term effects of fall-applied treatments.