DOWNY MILDEW.

Auckland Star, Volume LVII, Issue 204, 28 August 1926, Page 11

DOWNY MILDEW.

MENACE TO' VITICITI.TUB.E. , OUTBREAK IN HENDERSON . : . DISTRICT.. ~ ' '■' ; More than an ordinary share of trials and tribulations have beset vitieulturists in the Auckland province. They have experienced in the past the ravages, of phylloxera, , the small hemipterousous insect allied to: aphides, while this year an even .greater 'menace*'has made its appearance. This is downy, mildew, the worst fungus disease known to viticulturists, a disease that had its original home in- the United States.. one that some years ago spread to the-viticultural areas of France, Italy, Greece, and North Africa, leaving a train of ■; havoc behind it. A few yeare ago the disease made its appearance in a mild form in Auetralia, and now it ie New .Zealand's' turn. An outbreak of downy mildew—the first recorded in' New Zealand—occurred at Henderson and in -the -surrounding district during -the past > season;, and Since then searching investigations have been made by the officers of. ; the Department of Agriculture. It Jbas been definitely found that the field of infection is confined * within the limit! of a line drawn through Swanson on the north, Manukau Harbour and Auckland city on the south, -the upper Waitemata Harbour on the east, and the Taeman Sea on the west.

The outbreak of the disease first came under notice hr the early part of the present. year, and in all cakes was first seen in lower, parts of vineyards, near the bottom of gullies, close to creeks or swampy areas.. From what is known of the disease it appears to attack the young herbaceous part' of the Tine, principally 'the young leaves, shoots, flowers, and' immature grapes,- and it develops under the influence of heat and humidity; Its appearance is made evident by efflorescent spots or patches having the appearance of scattered salt on the under .side: of the leafund• directly under the oil spots. The downL can-be eiuiily removed, by rubbing a finger on flvand the facility with which it is removed distinguishes it from the white, spots of erinose - (Phytopus vitis), another vine pest,: but one that has jnot as yet'been reported in New ; Zealand. ; Naturally Auckland viticulturists have viewed the outbreak with, much concern as at the moment it is not known whether the pest is of the passing variety or, on the other hand, whether, it' has come to stay. The fungicide which has received the most universal approval , for the control of downy mildew is a Bordeaux mixture, and it has. already been proved that the real necessity is to maintain a continual supply of fungicide on the herbaceous parte of the affected vine, so that the spores arriving in the drop of water find some of the copper salts in solution,, and are thereby rendered innocuous.' .-.•■■