downy.pdf

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AVRDC International Cooperators' 
Fact Sheet
Crucifer Diseases
 
Downy Mildew
Peronospora parasitica
Worldwide
 
 
Damage Symptoms
Most crucifers are susceptible to downy mildew. It is 
particularly damaging to young cabbage seedlings and is 
considered to be oen of the more destructive foliar diseases 
of Chinese cabbage in Asia. Plants can be affected at any 
stage of development. 
The distinctive feature of the disease is production of a fluffy 
white growth found mostly on the underside of leaves. A yellow 
irregular shaped area appears on the upper side of the leaf 
opposite where sporulation occurs. On the surface of cabbage 
heads, the pathogen causes numerous sunken black spots 
ranging in size from necrotic flecks to 2 cm in diameter, with 
little or no sporulation. Cauliflower and broccoli floral heads 
develop dark brown internal streaks.
Conditions for Development
The fungus survives between crops as oospores or on 
cruciferous crop and weed plants. The fungus produces an 
abundance of sporangia that can be disseminated by wind 
and rain splash. Extended periods of leaf wetness caused by 
fog, rain, or dew are ideal for disease development. Downy 
mildew develops most rapidly when night temperatures are 
between 10 and 15°C. When night temperatures exceed 24°
C, disease development is greatly restricted.
 
Downy growth on lower 
leaf surface  
 
  
 
Internal darkening of 
broccoli floret from 
systemic invasion  
 
  
 
Internal darkening of 
cauliflower curd from 
systemic invasion 
Control
A few broccoli cultivars are resistant to downy mildew. Cultivars of other crucifers may 
vary in their reactions to downy mildew, but no high levels of resistance are available. 
Fungicidal treatment of crops is generally required if the disease is present and 
conditions are favorable for severe disease development.
http://www.avrdc.org/LC/cabbage/downy.html
Last updated: 2001. 
Information from: Vegetable Diseases: A Practical Guide. Lowell L. Black, AVRDC.
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