Preplant fumigation only temporarily reduces Northern root-knot nematode

Abstract

Context and purpose of the study – Management of plant-parasitic nematodes is typically focused on preplant fumigation, especially in a vineyard replant scenario. While the data are clear that this practice reduces nematodes immediately after application, which is useful in annually-cropped systems, does it have staying power in perennial cropping systems? The northern root-knot nematode Meloidogyne hapla reduces the overall lifespan and productivity of vineyards, but it does so over a long time period (slow, chronic decline). In two different commercial own-rooted V. vinifera vineyards, both undergoing vineyard replanting, we explored whether preplant fumigation reduced M. hapla densities in soils immediately after application. At one of these locations, we have explored the long-term effect of fumigation by monitoring the site for seven years post fumigation.

Material and methods – This trial was conducted at two commercial vineyards in eastern Washington State (USA). Both sites were previously planted to own-rooted V. vinifera, and were being replanted (in part) to own-rooted V. vinifera. Vineyard 1 – Old vines were removed in fall 2018, and the site was fumigated with 1,3-dichloropropene (1, 3-D) soil injection in spring 2019; nonfumigated areas were also included in the trial. The site was replanted in August 2019. Vineyard 2 – Older vines were treated with foliar glyphosate, and the soil fumigated with drip-applied metam sodium in fall 2014; nonfumigated areas were also included in the trial. Vines were removed over the winter, and the site was replanted in spring 2015. At both locations, soil samples for M. hapla enumeration were collected prior to fumigation, and every spring and fall post-fumigation. Nematode densities and nematode dosage were used to evaluate the effects of fumigation on subsequent nematode development on own-rooted V. vinifera vines.

Results – The fumigation with either 1,3-D or metam sodium had varying levels of efficacy at reducing M. hapla densities within 6 months of treatment (p = 0.31 Vineyard 1; p = 0.04 Vineyard 2) relative to non-fumigated plots. At both locations, in fumigated plots, total M. hapla densities reached preplant fumigation levels in own-rooted vines within 18 months post-fumigation (p = 0.94, Vineyard 1; p = 0.10 Vineyard 2). In Vineyard 2, after 7 years post-fumigation, there was no difference in nematode densities between fumigated and non-fumigated plots, and own-rooted vines showed equivalent levels of decline relative to vines planted on nematode-tolerant rootstocks that were also included in these trials. These results suggest that preplant fumigation alone is not a long-term control option for the management of M. hapla, and the adoption of resistant or tolerant rootstocks, along with other cultural control methods, will be needed for successful vineyard replanting.