Morphology and density of a crop influences its weed suppression ability

Abstract

Infection of grapevines by Phaeoacremonium species, thought to cause young vine decline, is currently causing concern to grape growers worldwide. Symptoms of the disease include chlorotic, sparse and stunted leaves, late bud-burst, uneven growth and undersized trunks, which show internal discolourations and frequently exude shiny, black, tarry substances ('black goo'). This study investigated prevalence of the disease within commercial vineyards in selected grape-growing areas. Grape growers, largely from Marlborough but also from Nelson, Canterbury and Gisborne, contributed vines with decline symptoms for further observation and isolation. Characteristic internal staining of vine trunks was found, usually below the graft union, in 84% of the 70 vine samples. Isolations onto selective agar found Phaeoacremonium spp., most commonly P. chlamydosporum, in 54% of vines and in 20 of the 27 vineyards sampled. Incidence may have been higher but 26% of wood specimens also contained other, fast-growing fungi which overgrew the wood tissues, interfering with attempts to isolate the slowgrowing Phaeoacremonium spp. Isolations from roots of the 33 most severely infected vines found 14 to be also infected with Cylindrocarpon destructans, which causes a root rot called 'black foot'. Further studies are needed into young vine decline and into the epidemiology and control of P. chlamydosporum.