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Spinach (Spinacia oleracea)-Downy Mildew

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Latest revision: 
March 2024
Image related to Spinach (Spinacia oleracea)-Downy Mildew
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.
Photo by Melodie Putnam, 2002
Image related to Spinach (Spinacia oleracea)-Downy Mildew
A closer view of the downy growth on the underside of a leaf.
Photo by Melodie Putnam, 2002.

By C.M. Ocamb and L.J. du Toit

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 in California spinach (CA 5 and 6 races) and another new race in Europe. This pathogen infects spinach and a few weedy Chenopodium species, but not lambsquarters. The downy mildew observed on lambsquarters 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.

Cultural control

  • If possible, plant in soil that has been out of spinach for several years.
  • Do not grow fall spinach crops in fields adjacent to spring crops or allow volunteer spinach to grow there.
  • Resistant varieties 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).
  • Treat seed for 25 min. in water at 122°F.
  • 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.

  • Actigard at 0.5 to 0.75 oz/A every 7- to 10-days controls disease by inducing host-resistance pathways. Gave good control in studies conducted by the University of Arizona. Do not apply within 7 days of harvest. 12-hr reentry.
  • CAA-fungicide (Carboxylic Acid Amides) formulations (Group 40) are labeled for spinach. Do not make more than two (2) sequential applications before alternating to a different mode of action.
    • 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 interval is 1 day. 4-hr reentry.
  • Copper products (Group M1) are not recommended as stand-alone materials and care should be taken to avoid build-up of copper in soils.
    • Badge SC at 1 to 2.25 pints/A on 7- to 10-day intervals. Preharvest interval is 0 days. 24-hr reentry for greenhouse use; 48-hr reentry for all other applications.
    • Champ WG at 1.0 to 1.58 lb/A on 7- to 10-day intervals. 48-hr reentry. O
    • Cueva at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. May be applied on the day of harvest. 4-hr reentry. O
    • Liqui-Cop at 3 teaspoons/gal water. H
  • Curzate 60 DF (Group 27) at 3.2 to 5 oz/A on 5- to 7-day intervals. Also special needs label for use on spinach seed crops in Oregon (SLN OR-150004) and Washington only (SLN WA-990021). Use only in combination with another registered protectant fungicide. Preharvest interval is 1 day. 12-hr reentry.
  • Mancozeb formulations (Group M3) are labeled.
    • Dithane F45 Rainshield at 1.5 quart/A on 7- to 10-day intervals can be used on seed crops only. Washington and Oregon only (SLN WA-220008, SLN OR-090016). 24-hr reentry.
    • Roper DF Rainshield at 2 lb/A on 7- to 10-day intervals can be used on seed crops only. Oregon and Washington seed crops only (SLN OR-130003, SLN WA-1300003). 24-hr reentry.
  • MetaStar 2E AG (Group 4) at 1 pints/A shanked in 21 days after planting or after first cutting. 48-hr reentry
  • MilStop SP (85% potassium bicarbonate) at 2 to 5 lb/A or 1 Tbsp/gal water on 7- to 14-day intervals. 1-hr reentry. H O
  • Orondis Gold 200 (Group 49) at 4.8 to 9.6 fl oz/A at planting, in-furrow or by drip. Do not apply more than two (2) sequential applications. Preharvest interval is 0 days. 4-hr reentry.
  • Orondis Ultra (Group 49 + 40) at 5.5 to 8 fl oz/A on 7- to 10-day intervals. Do not apply more than two (2) sequential applications. Preharvest interval is 1 day. 4-hr reentry.
  • Phosphonates (Group P7) can be very effective.
    • 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 mix with surfactants or foliar fertilizers. 24-hr reentry.
  • Presidio (Group 43) at 3 to 4 fl oz/A on 10-day intervals in combination with another fungicide that has a different mode of action. Preharvest interval is 2 days. 12-hr reentry.
  • Regalia (Group P5) at 1 to 4 quarts/A plus another fungicide on 5- to 10-day intervals. Does not benefit from the addition of an adjuvant. Preharvest interval is 0 days. 4-hr reentry. O
  • Ridomil Gold Copper at 2 lb/A. Do not apply within 3 days of harvest. 48-hr reentry.
  • Strobilurin fungicides (Group 11) are labeled for use. Do not make more than one (1) application of a Group 11 fungicide before alternating to a labeled fungicide with a different mode of action.
    • Quadris Flowable at 12 to 15.5 fl oz/A on 5- to 7-day intervals. 4-hr reentry.
    • Reason 500 SC at 5.5 to 8.2 fl oz/A. Do not apply within 2 days of harvest. 12-hr reentry.
  • Trilogy at 0.5% to 1%. Not labeled for use in Oregon. Do not use above 90°F or when plants are under heat or moisture stress. Do not use when foliage is wet as good coverage is essential. Poor control as a stand-alone product. 4-hr reentry. O
  • Zampro (Group 40 + 45) at 14 fl oz/A for no more than three (3) applications per season. Do not apply more than two (2) applications before alternating to a fungicide with a different mode of action. Preharvest interval is 0 days. 12-hr reentry.

Biological control Efficacy in Oregon unknown.

  • Actinovate AG at 3 to 12 oz/A as a foliar spray on 7- to 14-day intervals. 4-hr reentry. O
  • Actinovate Lawn & Garden at 0.5 to 1 teaspoon/gal water. H O
  • Double Nickel LC at 0.5 to 4.5 pints/A on 3- to 10-day intervals. Can be applied the day of harvest. 4-hr reentry. O
  • LifeGard WG (Group P6) at 1 to 4.5 oz/A on 7- to 14-day intervals for activating plant resistance. Refer to label for appropriate rate per application volume. Preharvest interval is 0 days. 4-hr reentry. O
  • Romeo at 0.45 to 0.68 lb/A on 7- to 10-day intervals starting prior to infection. Preharvest interval is 0 days. 4-hr reentry. O
  • Sonata at 2 to 4 quarts/A on 7- to 14-day intervals for disease suppression. Can be applied up to and on the day of harvest. 4-hr reentry. O
  • Stargus at 6 to 8 fl oz per 1,000 ft row as an in-furrow treatment, 3 to 4 quarts/A as a soil drench (drip or chemigation) on 10- to 21-day intervals, or 2 to 4 quarts/A as a foliar spray on 7- to 10-day intervals. Preharvest interval is 0 days. 4-hr reentry. O

References Koike, S.T. Update on spinach downy mildew. 1999. Monterey County Crop Notes, University of CA Coop Ext.

Irish, B.M., Correll, J.C., Koike, S.T., and Morelock, T.E. 2007. Three new races of the spinach downy mildew pathogen identified by a modified set of spinach differentials. Plant Disease 91:1392-1396.

Matheron, M.E., Correll, J.C., Porchas, M. and Feng, C. 2019. Evaluation of fungicides for management of downy mildew of spinach, 2018. Plant Disease Management Reports 13:V044.