Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Spinach (Spinacia oleracea) -- Downy Mildew
 
Cause: Peronospora farinosa f. sp. spinaciae (formerly P. effusa), a fungus-like microorganism that overwinters on dead spinach plants, old plant debris, and volunteer spinach; it also can be seedborne. Downy mildew develops during cool, wet conditions. Dense plantings promote the disease by promoting wet conditions. Infections are systemic. Ten races have been reported with two new races found in California spinach (CA 5 and 6 races) and another in Europe. This pathogen infects spinach and a few weedy Chenopodium species, but not lambs quarters. The downy mildew observed on lambs quarters does not infect spinach.
Symptoms: Pale yellowish spots with a gray to purple downy growth on leaf undersurfaces are typical in wet weather. Infections may be scanty or numerous, often growing together. Severely infected plants are stunted or die. Downy mildew leaf infections can cause rot of infected leaves packed in bags and cartons

Note the yellowish coloration of the upper surface of the leaves on the left. A downy growth is visible on the underside of the two leaves on the right.

A closer view of the downy growth on the underside of a leaf.
 
Cultivar Resistance: Resistant cultivars and the races they resist: 'Nores', 'Duet', 'Early Hybrid 7' (1, 2); 'Dixie Market', 'Hybrid 424' (1, 2); 'Polka' (1, 2, 3); 'St. Helens' (1, 2, 3); 'Resistoflay' (1, 2); 'Baker' (1, 2, 3); 'Jade' (1, 2, 3); 'Olympia' (1, 2, 3); 'Rainier' (1, 2, 3); 'Shasta' (1, 2, 3); 'Woster' (1, 2, 3); 'Melody' (1, 2); 'Debut' (1, 2, 3); 'Meridian' (1, 3).
Cultural control:

  1. If possible, plant in soil that has been out of spinach for several years.
  2. Do not grow fall spinach crops in fields adjacent to spring crops or allow volunteer spinach to grow there.
  3. Treat seed for 25 min in water at 122oF (50oC).
  4. After harvest of spinach seed crops, incorporate residues and volunteer spinach into the soil to reduce the risk of inoculum overwintering on volunteers and infested residues.
Chemical control: Apply fungicides regularly early in the season to protect plants from infection.

  1. Agri-fos at 0.5 gal/A in 40 gal water. Ensure spray coverage is adequate to wet the whole plant. During warm, wet conditions, applications on 7- to 10-day intervals may be needed. 4-hr reentry.
  2. Aliette WDG at 2 to 5 lb/A. Do not apply in less than 10 gal water/A or within 3 days of harvest. Speckling can occur if solution pH is below 6. Do not use within a few days of a copper application. Do not mix with surfactants or foliar fertilizers. 12-hr reentry.
  3. Curzate 60 DF at 3.2 oz/A on 5- to 7-day intervals. For use on spinach seed crops in Washington only (SLN WA-990021). Use only in combination with another registered protectant fungicide. 12-hr reentry.
  4. Kop-R-Spray at 1.5 teaspoons/gal water.
  5. MetaStar 2E AG at 1 pints/A shanked in 21 days after planting or after first cutting. 48-hr reentry
  6. MilStop (85% potassium bicarbonate) at 2 to 5 lb/A. 1-hr reentry.
  7. Nu Cop 50 WP at 2 to 4 lb/A on 7- to 10-day intervals. Do not apply within 1 day of harvest. 24-hr reentry.
  8. Quadris at 12 to 15.5 fl oz/A on 5- to 7-day intervals. Do not apply more than one (1) foliar application of Quadris or other Group 11 fungicide before alternating to a labeled fungicide with a different mode of action. 4-hr reentry.
  9. Revus at 8 fl oz/A on 7- to 10-day intervals. Do not make more than two (2) foliar applications of Revus before alternating to a labeled fungicide with a different mode of action (non-group 40). Preharvest inter-val is 1 day. 12-hr reentry.
  10. Ridomil Gold Copper at 2.5 lb/A. Do not apply within 21 days of harvest. 48-hr reentry.
  11. Topaz at 1 to 4 quarts/A in 100 gal water on 2- to 3-week intervals. 4-hr reentry.
Biological control: Efficacy in Oregon unknown.
  1. Sonata at 2 to 4 qt/A on 7- to 14-day intervals for disease suppression. Can be applied up to and on the day of harvest. 4-hr reentry.
References:
Koike, S. T. Update on spinach downy mildew. 1999. Monterey County Crop Notes, University of CA Coop Ext.
Irish, B.M., J.C. Correll, S.T. Koike, and T.E.Morelock, 2007. Three new races of the spinach downy mildew pathogen identified by a modified set of spinach differentials. Plant Disease 91:1392-1396.
Content edited by: C.M. Ocamb and L.J. du Toit on January 1, 2009
 
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