Pacific Northwest Plant Disease Management Handbook

Chrysanthemum-Powdery Mildew

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Latest revision: 
March 2024

Cause Golovinomyces cichoracearum (formerly Erysiphe cichoracearum), and G. chrysanthemi, fungi reported from Washington that produces airborne spores only on living chrysanthemum plants. High humidity, crowding, and cool weather favor the disease.

Symptoms Whitish-gray powdery growth on leaves, stems, and buds. Severely affected leaves become narrow, stunted, and stiff. Lower leaves may drop.

Cultural control Early detection with regular scouting is very important.

  • Keep susceptible cultivars isolated.
  • Space plants far enough apart to ensure good air circulation.
  • Pick off and burn affected leaves, if practical.
  • Keep greenhouse humidity low.

Chemical control Scout plants regularly and use fungicides just before or when first symptoms appear. Alternate or tank-mix products from different groups that have different modes of action. Limit the use of any one group during crop production.

  • Avelyo at 3 to 5 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • Bicarbonate-based products. Might be used to 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.
  • Disarm 480 SC at 1 to 4 fl oz/100 gal water. Group 11 fungicide. 12-hr reentry.
  • Eagle 20 EW at 8 fl oz/100 gal water. Group 3 fungicide. 24-hr reentry.
  • 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.
  • JMS Stylet Oil at 1 oz/1 gal water. Do not use with or near a sulfur application. Do not use during freezing temperatures, above 90°F, or when plants are under heat or moisture stress. Do not use when foliage is wet as good coverage is essential. 4-hr reentry. O
  • Myclobutanil 20 EW T&O at 8 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 production only. Group 5 fungicide. 12-hr reentry.
  • Postiva at 10 to 28 fl oz/100 gal water. Group 3 + 7 fungicide. 12-hr reentry.
  • Regime at 20.5 to 45.7 fl oz/A. Reapply if rain occurs within 12 hours 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
  • Sulfur (90%) at 3 Tbsp/gal water. Avoid using sulfur during hot periods or on open flowers because it may cause bleaching. Group M2 fungicide. 24-hr reentry. H O
  • Terraguard SC at 4 to 8 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • Tourney EZ at 1 to 4 oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • 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. Efficacy in the Pacific Northwest is unknown. 4-hr reentry. O

Reference Trolinger, J.C., McGovern, R.J., Elmer, W.H., Rechcigl, N. A., and Shoemaker, C. M. 2018. Diseases of Chrysanthemum. In McGovern, R.J. and Elmer, W.H. (eds.) Handbook of Florists' Crops Diseases. Springer Int.

Pscheidt, J.W., and Ocamb, C.M. (Senior Eds.). 2024 Pacific Northwest Plant Disease Management Handbook.
© Oregon State University.

Use pesticides safely!

  • Wear protective clothing and safety devices as recommended on the label. Bathe or shower after each use.
  • Read the pesticide label—even if you’ve used the pesticide before. Follow closely the instructions on the label (and any other directions you have).
  • Be cautious when you apply pesticides. Know your legal responsibility as a pesticide applicator. You may be liable for injury or damage resulting from pesticide use.

Trade-name products and services are mentioned as illustrations only. This does not mean that the participating Extension Services endorse these products and services or that they intend to discriminate against products and services not mentioned.

H - Home garden packaging commonly available.     O - Acceptable in organic production.