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.
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.
No biological control strategies have been developed for downy mildew.
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.
Strains of P. parasitica insensitive to metalaxyl are widespread, and fungicides with other modes of action should be used if insensitive strains are present or to delay their occurence.
Product List for Downy Mildew:
Pesticide |
Rate per Acre |
Application Frequency (days) |
Remarks |
|
Azoxystrobin |
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Quadris |
6.2-15.4 fl oz |
7-14 days |
Maximum of 3 applications or 2.88 quarts per season; Do not make more than 1 application of Quadris before rotating to a fungicide with a different mode of action; 0 day PHI |
Copper Fungicides |
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|
Basicop |
3-4 lb |
7-14 days |
Crop injury can occur |
|
Champ Dry Prill |
0.33-0.66 lb |
7 days |
Crop injury can occur |
|
Champ Formula 2 |
1.33 pt |
5-7 days |
Crop injury can occur |
|
Copper-Count-N |
1-3 qt |
7-10 days |
Crop injury can occur |
|
Cuprofix Disperss |
1.5-2.5 lb |
5-10 days |
Crop injury can occur |
|
Top Cop + S |
4 pt |
7-10 days |
Crop injury can occur |
|
Metalaxyl/Methoxonam |
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|
Allegiance FL |
1.5-3.0 fl oz |
Seed treatment |
May provide some suppression |
|
Allegiance LS |
2.4-4.9 fl oz |
Seed treatment |
May provide some suppression |
|
Apron XL LS |
1.28 fl oz |
Seed treatment |
May provide some suppression |
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The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. |
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Categories: Canola and Mustard, Disease, Downy Mildew
Date: 12/30/2004