Impact of citrus nematode (Tylenchulus semipenetrans) densities in soil on yield of grapevines (Vitis vinifera 'Shiraz') in south-eastern New South Wales

Abstract

'Shiraz' is a popular red wine grape variety grown in NSW, Australia, and is susceptible to citrus nematode (Tylenchulus semipenetrans). The extent of damage, particularly yield loss, or the damage threshold level of T. semipenetrans in 'Shiraz' is not known. In this study we investigated the population dynamics and the effects of a range of population densities of T. semipenetrans on yield of 'Shiraz' in a naturally infested vineyard across three growing seasons. Results showed that the population density of T. semipenetrans J2 in soil did not increase or decrease consistently during the trial period. However, the population densities varied significantly (P < 0.05) between the temporal seasons in a year and were in order of summer > spring > autumn > winter. Yield from vines with T. semipenetrans J₂ population densities greater than 9,000·kg^-1 dry soil (average population over 11,000·kg^-1 dry soil) was 15 % lower compared to vines with 500-3,000 (average 932) T. semipenetrans J₂·kg^-1 dry soil in 2004 but not in 2001 and 2003. Regression analysis showed a linear trend (r = -0.36) on yield decrease with the increase of T. semipenetrans densities in soil in 2004, when the 'Shiraz' vines were eight years old. Pruning weight was reduced by 18.7 to 22.9 % when nematode population densities were greater than 12,000·kg^-1 dry soil (average population over 19,000·kg^-1 dry soil).