HPIPM:Downy Mildew CC

Author: Howard F. Schwartz and David H. Gent

Taxonomy

Domain	Eukarya
Kingdom	Chromista
Phylum	Oomycota
Class	Oomycetes
Order	Peronosporales
Family	Peronosporaceae
Genus	Hyaloperonospora

Scientific Name

Hyaloperonospora parasitica

Scientific Name Synonyms

Peronospora parasitica

Common Name

downy mildew

Identification and Life Cycle

Downy mildew is caused by the fungus-like organism Peronospora parasitica, and can attack broccoli, cauliflower, cabbage, and brussel sprouts. Infection occurs when soilborne resting structures called oospores germinate and produce sporangia under moist, cool conditions. Sporangia are produced on the underside of leaves in the evening and are released during the day as leaves dry. The windblown sporangia land on leaves and directly penetrate leaves and flowers. The pathogen survives between cole crops in the soil as oospores.

Plant Response and Damage

Disease symptoms first appear as light green or slightly chlorotic lesions that become yellow or necrotic after sporulation. Lesions are angular and variable in size, but are often bounded by large veins. The bottom sides of leaves develop a fluffy or downy appearance from sporulation during cool, moist conditions. Old lesions become necrotic and translucent after invasion by secondary saprophytes. Seedlings may be killed or develop dark brown vascular systems from severe infections, but older plants are rarely killed. The disease can be devastating under cool, moist conditions.

Biological Control

No biological control strategies have been developed for downy mildew.

Cultural Control

Resistant or tolerant varieties should be planted where available. Many strains of the pathogen exist, and specific host resistance may not be effective against all races of the pathogen. Subsurface drip irrigation may provide some disease suppression as compared to furrow or sprinkler irrigation. If possible, time irrigations to end before dusk to prevent extended periods of leaf wetness.

Chemical Control

Strains of P. parasitica insensitive to metalaxyl are widespread, and fungicides with other modes of action should be used if insensitive strains are present.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.