Black foot disease in South African vineyards and grapevine nurseries

Over the last few years a drastic reduction has been noted in the survival rate of vine cuttings in nurseries, as well as in young vineyards in the Western Cape Province of South Africa. The low average take percentages of young vines can be attributed to several factors, including fungal, bacterial and viral diseases, insect and nematode pests, abiotic factors, as well as nutritional deficiencies and toxicities. Cylindrocarpon spp., which cause black foot disease of grapevine were found to be associated with the decline of young vines in South Africa. Results obtained from the diagnostic service at ARC Infruitec-Nietvoorbij (Disease Management Division) showed that Cylindrocarpon spp. were isolated from 52%, 22% and 29% of diseased vines during 1999-2002, 2002-2003 and 2003-2004, respectively. However, it was unclear how and where these infections occurred. Very little information is available regarding the aetiology and epidemiology of the fungi believed to be involved in black foot disease. Diseased grapevines delivered for diagnosis were typically less than 5 years old and in some instances symptoms even appeared during the first year of planting. Diseased plants display an array of decline symptoms. In vineyards, the first visible symptoms are usually delayed or absence of budding. Subsequently shoots develop abnormally (shortened internodes and small discoloured leaves) which may dry and even die during summer. When symptomatic plants are removed from the soil, inspection of the roots may reveal the presence of grey to black necrosis which ultimately leads to the underdevelopment of the entire root system. Further root abnormalities include the development of secondary root crowns with roots growing parallel to the soil surface. Internal symptoms include brown-black discoloration of xylem vessels originating from the base of the rootstock, brown-black discoloration in roots, and necrosis from the bark to the centre of roots and rootstocks (Fourie & Halleen, 2001).
The purpose of this communication is to provide a short overview of the results obtained from research conducted during the past 5 years. The primary aims of research have been (1) to conduct nursery surveys in order to determine which fungi are involved in the decline phenomenon, with special reference to the involvement of Cylindrocarpon spp., (2) to identify the organisms believed to be the causal organisms of black foot disease, and (3) the development of control and/or management strategies to prevent or eradicate Cylindrocarpon infections.