Effect of Methyl Bromide Alternatives on Plant Parasitic Nematodes and Grape Yield under Vineyard Replant Conditions

Abstract

Preplant fumigants and nematode-resistant rootstocks were evaluated as alternatives to methyl bromide in a vineyard replant situation. Two months after fumigation, Thompson Seedless on its own roots, Merlot on 1103 Paulsen rootstock, and Thompson Seedless on Freedom rootstock were planted. The study revealed that 1,3-dichloropropene plus chloropicrin (578 kg/ha shank injected), iodomethane plus chloropicrin (515 kg/ha shank injected or 448 kg/ha drip applied), and propargyl bromide (221 kg/ha shank injected or 207 kg/ha drip applied) generally controlled root-knot (Meloidogyne spp.) and citrus (Tylenchulus semipenetrans) nematodes as well as methyl bromide (507 kg/ha shank injected) over an 8-year evaluation period. Sodium azide (336 kg/ha drip applied followed with either a water cap or tarp), metam sodium (124 kg/ha applied with microspray sprinklers), and chloropicrin alone (448 kg/ha drip applied) were less effective. In general, the effect of fumigants on nematode control was very evident in the own-rooted Thompson Seedless. The 1103P rootstock was partially tolerant to root-knot and citrus nematodes for the first 3 to 4 years, respectively, before nematode populations began to rebuild. In contrast, Freedom rootstock proved to be highly resistant and kept root-knot nematode populations low during the 8-year evaluation. However, preplant fumigation is still likely to be required in fields where citrus nematodes are present. Application of propargyl bromide and replanting with Merlot on 1103P rootstock was the only fumigant-rootstock combination that resulted in grape yield similar to methyl bromide. However, this effect was observed only during the first four years of fruit production. The other fumigant and cultivar combinations did not result in yield differences compared to the untreated control.