Epidemiology of grapevine anthracnose and downy mildew in an auckland, new zealand vineyard

Abstract

Epidemics on vine leaves of anthracnose, caused by Elsinoe ampelina Shear, and of downy mildew, caused by Plasmopara viticola (Berkeley & Curtis ex de Bary) Berlese & de Toni, were studied in an Auckland vineyard during 11 seasons, 1971/72-1981/82. Primary infection by E. ampelina, from conidia on cane lesions, occurred in late September-early October, within 4 weeks from budburst. An epidemic failed to develop in only one season, 1972/73, in which rainfall was unusually low. Leaves that escaped infection in their first 4 weeks generally remained free from anthracnose thereafter, and the most severe epidemics occurred in seasons in which the intervals between rain periods were short Primary infection by P. viticola, presumed to be from oospores, occurred in November-early January, corresponding to the period from 2 weeks before anthesis to fruit set. Primary infections resulted in only small numbers of lesions. In 8 of the 11 seasons there was no downy mildew at the end of December on canes selected for detailed recording. Leaves did not become resistant with age, and in two seasons when epidemics did not begin until autumn most leaves eventually became mildewed. Rainfall of <1 mm could provide moisture needed for infection by P. viticola. No downy mildew occurred in the driest season. In three seasons severe epidemics developed over periods of 50 days in summer/autumn with rainfall for the period ranging from 36 to 58 mm. In two seasons downy mildew became established in summer but epidemics failed to develop in 50 days despite rainfall in the periods of 99 and 234 mm, and temperatures similar to those in the epidemic seasons. Fungicide sprays protective against anthracnose should be applied from budswell to fruit set. Sprays to control downy mildew need not be applied at the beginning of the season, and there are prospects for using a monitoring system as a basis for a control programme. © 1992 The Royal Society of New Zealand.