Downy mildew of spinach is caused by the fungus-like organism Peronospora farinosa f. sp. spinaciae (syn.= P. effusa). Downy mildew is a very common and often destructive disease of spinach in the High Plains during cool, wet conditions. The pathogen is disseminated within and among fields by wind and splashing water droplets. At least four races of the downy mildew pathogen have been identified, but all races of the pathogen are not present in the High Plains spinach production regions. The pathogen survives between spinach crops in and on dead spinach plants, crop residues, volunteer spinach and some weeds, and in infested seed.
Downy mildew symptoms first appear as pale yellowish spots with a gray to purple downy growth on leaf undersurfaces. This downy growth is most apparent during wet weather. Infections may be scattered or numerous, but individual lesions often coalesce. Severely infected plants are stunted or die. Downy mildew can reduce both spinach yield and quality, and can be quite damaging to susceptible cultivars during cool, wet weather.
Biological control strategies have not been developed for downy mildew.
Several resistant varieties have been developed and should be planted if suitable for your production and marketing needs. Varieties need to be selected carefully to match the prevalent pathogenic races in your specific production region. Practice a three-year or longer crop rotation to nonhosts such as small grains and corn. Reduce prolonged periods of leaf wetness by increasing row spacing, orientating rows parallel to the prevailing wind direction, and avoiding overhead irrigation. If possible, time irrigation to end before dusk to avoid extended periods of leaf wetness. Promptly and thoroughly incorporate crop residues and volunteer spinach to reduce pathogen survival and overwintering.
Chemical controls are most effective when integrated with sound cultural control practices. Copper-based fungicides may leave unattractive residues on leaves and make them unmarketable.
Product List for Downy Mildew:
Pesticide |
Product per Acre |
Application Frequency (days) |
Remarks |
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Acibenzolar |
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Actigard 50WG |
0.5-0.75 oz |
7-10 days |
Maximum of 3 applications or 2.25 ounces per season; Do not apply to plants under stress or young seedlings; 7 day PHI |
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Copper Fungicides—not all formulations available are listed |
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Champ DP |
1.33-2.66 lb |
7-10 days |
Can cause leaf flecking |
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Copper-Count-N |
3 pt |
7-10 days |
Can cause leaf flecking |
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Cuprofix Disperss |
2.5-4 lb |
7-10 days |
Can cause leaf flecking |
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Kocide 2000 |
1.5-2.25 lb |
7-10 days |
Can cause leaf flecking |
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Kocide 3000 |
0.75-1.25 lb |
7-10 days |
Can cause leaf flecking |
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Nordox |
2-3 lb |
7-10 days |
Can cause leaf flecking |
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Nu-Cop 3L |
1.33-2.66 pt |
7-10 days |
Can cause leaf flecking |
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Tri-Basic Copper |
4 pt |
7-10 days |
1 day PHI |
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Fosetyl-Al |
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Aliette 80 |
2-5 lb |
7-21 days |
Maximum of 7 applications; 3 day PHI |
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Mefoxonam |
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Ultra Flourish |
8 oz-4 pts |
Pre-plant incorporated drench or 7” soil band |
2 layby applications can be shanked in; 21 day PHI |
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Ridomil Gold EC |
1-2 pt |
Pre-plant incorporated soil drench or soil band (a 7” band is recommended) |
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Ridomil Gold GR |
20-40 lb |
Pre-plant incorporated soil drench or soil band (a 7” band is recommended) |
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Ridomil Gold/Copper |
1 pack/2 acres |
14 days |
Maximum of 2 applications; 21 day PHI |
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Neem |
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Trilogy |
2 pt |
7-14 days |
Maximum of 2 gallons per season; 0 day PHI |
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Phosphorous Acid |
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Agri-Fos |
0.5 gal in 200 gallons water |
7-10 days |
Ensure thorough coverage of all foliage |
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Potassium Bicarbonate |
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Armicarb 100 |
2.5-5 lb |
5-14 days |
Apply in at least 20 gallons per acre; 0 day PHI |
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Strobilurin |
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Amistar |
2-5 oz |
5-14 days |
Maximum of 4 applications; rotate with a fungicide with a different mode of action; 0 day PHI |
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Quadris |
6.2-15.4 fl oz |
5-14 days |
Maximum of 4 applications; rotate with a fungicide with a different mode of action; 0 day PHI |
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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: Spinach, Diseases, Downy Mildew, Blue Mold
Date: 04/01/2007