Downy mildew

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Downy mildew
Grape Downy Powdery Mildew.jpg
A grape leaf showing downy mildew and powdery mildew
Scientific Classification
Kingdom: Chromalveolata
Phylum: Heterokontophyta
Class: Oomycetes
Order: Peronosporales
Family: Peronosporaceae

Downy mildew refers to any of several types of oomycete microbes of the Peronosporaceae family that are a particular problem for growers of brassicas, grapes and vine-type vegetables.

Cucurbit downy mildew (caused by Pseudoperonospora cubensis) is specific to cucurbits (e.g. pumpkin, squash, courgette). The disease is one of the most important diseases of cucurbits worldwide.

A serious disease in cool, damp seasons.

Symptoms[edit]

The initial symptoms of downy mildew appear on leaves as light green to yellow spots, then as it develops it becomes a downy grey mould. Leaves slowly die back and shrivel from the tips.[1] Onion bulbs infected become soft and are not suitable for storage.

Treatment[edit]

None. Should the disease be confirmed on site, immediately dispose of diseased material in sealed bags or bins and arrange for it to be destroyed.[2]

Prevention[edit]

Good practice[2]:

  • Try to ensure any starting plant material is disease free.
  • Provide good air circulation and ventilation in glasshouses.
  • Try to avoid long periods of high humidity and leaf wetness.
  • Avoid watering crops late in the day.
  • Apply a routine preventative fungicide programme to minimise disease risk, especially during periods when environmental conditions are favourable for downy mildew infection.
  • Practice good nursery hygiene by cleaning up plant debris between crops and at the end of the season and use appropriate disinfectants.

Examples[edit]

References[edit]

  1. Hessayon, D.G. (2009). The Vegetable & Herb Expert. Transworld Publishers, London. p. 75. ISBN 9780903505468
  2. a b McPherson, M. and Brough, W. (2009) "Good Horticultural Practice for the Prevention and Control of Impatiens Downy Mildew (Plasmopara obducens)". Agriculture and Horticultural Development Board. Retrieved 2010-07-17.
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