|Ajwa, Husein - UC DAVIS|
Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 16, 2005
Publication Date: December 1, 2006
Citation: Schneider, S.M., Ajwa, H.A., Trout, T.J. 2006. Chemical alternatives to methyl bromide for vineyard replant conditions. American Journal of Enology and Viticulture, 57(2): 183-193. Interpretive Summary: 'Vineyard Replant Disorder' is a generic lack of vigorous growth of a young vineyard when planted into land previously planted to a vineyard. There are many potentially contributing factors including populations of soilborne pathogens and nematodes, as well as not-yet-identified factors. The combination of contributing factors will vary from vineyard to vineyard. Methyl bromide has commonly been used to control replant disorder. Methyl bromide will be banned beginning in Jan 2005 except for specific uses. Vineyard growers will need alternatives to methyl bromide for replant disorder. Our field trials showed that propargyl bromide, 1,3-dichloropropene, and iodomethane provided nematode control comparable to methyl bromide during the first growing season. Plant growth, however, was still greater in plots fumigated with methyl bromide. These results demonstrate that although alternatives to methyl bromide for nematode control in sandy loam soils are available, these materials do not prevent the reduction in first year vine growth due to replant disorder. Additional research is needed to determine the impact of this reduction in growth to the on-going productivity of the new vineyard and to identify the unknown factors contributing to vineyard replant disorder.
Technical Abstract: Vineyard replant disorder is a disease of unknown etiology, currently controlled by methyl bromide fumigation. While not all the components of the disease are known, plant-parasitic nematode densities are often high in vineyard replant soils. Alternatives to the broadly effective general biocide, methyl bromide, will be needed for vineyards replanted after January, 2005 when import and manufacture of methyl bromide is banned except for exempted quarantine uses and approved critical uses. Two field trials were conducted in vineyards that had been planted to own-rooted Thompson Seedless grapes for 70 to 85 years and were known to support populations of plant-parasitic nematodes. In a randomized block design with five or six replicates per trial, shank-injected and/or drip-applied propargyl bromide, iodomethane + chloropicrin, and 1,3-dichloropropene + chloropicrin provided control of plant-parasitic nematodes at the end of the first growing season similar to that achieved with methyl bromide, but drip-applied sodium azide did not suppress nematodes below detection threshold levels under vineyard replant conditions. Vine growth during the first growing season responded more differentially to the treatments than did nematode population. Although vine growth in the treated plots was greater than in the untreated plots for most treatments, growth was not as vigorous as in plots fumigated with methyl bromide. Alternatives to methyl bromide for nematode control in sandy loams soils were documented, but acceptable alternatives for the management of the more complex vineyard replant disorder are more elusive.