1. Plant Disease
  2. Host and Disease Descriptions

Zinnia-Powdery Mildew

  • Facebook logo
Latest revision: 
March 2024
Image related to Zinnia-Powdery Mildew

Powdery mildew can cover leaves and stems late in the growing season.

Jay W. Pscheidt, 2014.
Image related to Zinnia-Powdery Mildew

Heavy mycelial growth can be seen late in the growing season.

Jay W. Pscheidt, 2014.

See:

Greenhouse Plants, Ornamental - Powdery Mildew

Cause Golovinomyces spadiceus (formerly Erysiphe cichoracearum), a fungus. Overwinters as either chasmothecia or conidia on infected plants. The conidia are readily wind disseminated. Chasmothecia develop within the external hyphae and form appendages late in their development. The disease has been rarely noted on the Crystal and Star series of plants.

Symptoms White powdery fungal growth on leaves, flowers or stems, especially late in the season in partially shaded locations. Leaves die from the base of the plant upwards and plants lose vigor and stop growing.

Cultural control

  • The cultivars Old Mexico, Orange Star, Pinwheel, and Star White were resistant in a Sunset magazine trial. The Profusion series of zinnia also is reported resistant.
  • Plant in full sun.

Chemical control Spray at 7- to 10-day intervals starting when mildew first appears. Early detection and scouting aid overall control. Alternate or tank-mix products from different groups that have different modes of action. Limit the use of any one group during crop production.

  • Armada 50 WDG at 3 to 9 oz/100 gal water. Do not use a silicone-based surfactant. Not for nursery or greenhouse use. Group 3 +11 fungicide. 12-hr reentry.
  • Avelyo at 3 to 5 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • Banner MAXX at 5 to 8 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • Bicarbonate-based products. Might supplement a normal program when powdery mildew is first observed. Do not mix with acidifying agents. Thorough coverage is essential. O
    • MilStop (85% potassium bicarbonate) at 2.5 to 5 lb/A in the field or 1.25 to 5 lb/100 gal water in the greenhouse. Oregon and Washington only. 1-hr reentry.
    • Monterey Bi-Carb Old Fashioned Fungicide at 4 teaspoons/2 gal water H
  • Broadform at 2 to 4 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
  • Compass 50 WDG at 1 to 2 oz/100 gal water. Do not use organosilicate additives. Group 11 fungicide. 12-hr reentry.
  • Daconil Weather Stik at 1.38 pints/100 gal water. Registered, but overall efficacy most likely is low. Group M5 fungicide. 12-hr reentry.
  • Eagle 20 EW at 6 to 12 fl oz/100 gal water. May cause some growth regulation effects. Group 3 fungicide. 24-hr reentry.
  • EcoSwing at 2.5 to 3.2 oz/10 gal water. Poor control. Group BM01 fungicide. 4-hr reentry. O
  • Fame SC at 1 to 4 fl oz/100 gal water. Group 11 fungicide. 12-hr reentry.
  • Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-hr reentry.
  • Insignia SC at 3 to 6 fl oz/100 gal water. Do not use with organosilicate-based adjuvants. Use preventively only. Group 11 fungicide. 12-hr reentry.
  • Myclobutanil 20 EW T&O at 6 to 12 fl oz/100 gal water plus spreading agent. May observe a PGR effect. Group 3 fungicide. 24-hr reentry.
  • Orkestra at 6 to 8 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
  • Ortho Rose & Flower Disease Control at 2 fl oz/gal water. Group 3 fungicide. H
  • Pageant at 6 to 12 oz/100 gal water. Do not use with organosilicone-based adjuvants. Group 7 + 11 fungicide. 12-hr reentry.
  • Pipron at 4 to 8 fl oz/100 gal water plus a surfactant. Greenhouse use only. Group 5 fungicide. 12-hr reentry.
  • Propiconazole-based products. Group 3 fungicides.
    • Banner MAXX at 5 to 8 fl oz/100 gal water. 12-hr reentry.
    • Infuse Systemic Disease Control at 1 Tbsp/gal water. H
  • Regime at 20.5 to 45.7 fl oz/A. Reapply if rain occurs within 12 hr of original application. Group BM01 fungicide. 4-hr reentry.
  • Safer Garden Fungicide (Ready To Use 0.4% sulfur) thoroughly sprayed over the entire plant. Do not use when the temperature is over 85°F or within a few weeks of an oil spray. H
  • Seido at 4 to 5 fl oz/100 gal water plus an adjuvant. Group 50 fungicide. 4-hr reentry.
  • Sil-Matrix at 1 to 4 quarts/100 gal water plus a nonionic surfactant. 4-hr reentry. O
  • Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 1 fl oz/gal water. Group 3 fungicide. H
  • Terraguard SC at 4 to 8 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • Thiolux (80% sulfur) at 3 to 10 lb/A. Group M2 fungicide. 24-hr reentry. O
  • Trinity at 4 to 12 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.

Biological control

  • Cease or Rhapsody (Bacillus subtilis strain QST 713) at 2 to 8 quarts/100 gal water. Active ingredient is a small protein. 4-hr reentry. O

Reference Szopinska, D. 2018. Diseases of Zinnia. In McGovern, R.J. and Elmer, W.H. (eds.) Handbook of Florists' Crops Diseases. Springer Int.