Chrysanthemum-Gray Mold

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Cause Botrytis cinerea, a fungus. Botrytis blight is a disease of greenhouse-grown chrysanthemums. The fungus survives in plant debris as sclerotia. Spores spread by overhead irrigation and by air, favored by high humidity and temperatures of 50°F to 70°F. Warm days followed by cool nights encourages condensation on flowers which favors disease development. Wounded or senescent tissue is most likely to be infected.

Symptoms Brown water-soaked spots on chrysanthemum petals and leaves. First symptoms usually are on outer, older florets. Later, a powdery grayish brown mass of fungal spores covers affected parts. Lower senescent leaves may rot, and if the fungus gets into the stem, it may girdle the stem.

Cultural control

  • Provide good air circulation-space plants apart.
  • Remove and destroy affected leaves as soon as noticed. Dispose of all plant debris promptly.
  • Avoid overhead watering.

Chemical control Use as a foliar spray in conjunction with cultural control methods. Tank-mix and/or alternate products from different groups with different modes of action to prevent the buildup of resistant fungi. Limit the use of any one group during crop production.

  • Astun at 10 to 17 fl oz/100 gal water. Group 7 fungicide. 12-hr reentry.
  • Bonide Captan 50 WP may be used in Oregon home gardens at 2 Tbsp/gal water. H
  • Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water. H
  • Captan 80 WDG at 1.5 lb/100 gal water. Group M4 fungicide. 48-hr reentry.
  • Chipco 26019 N/G at 1 to 2.5 lb/100 gal water. Group 2 fungicide. 12-hr reentry.
  • Copper-Count-N at 1 quart/100 gal water. Discolored foliage or blooms have been noted. Group M1 fungicide. Oregon only. 48-hr reentry general or 24-hr reentry for greenhouse.
  • Daconil Weather Stik at 1.4 pints/100 gal. Avoid blooms. Group M5 fungicide. 12-hr reentry.
  • Decree 50 WDG at 0.75 to 1.5 lb/100 gal water. Group 17 fungicide. 12-hr reentry.
  • Emblem at 2 to 4 fl oz/100 gal water. Use with oils or adjuvants may cause plant damage. Group 12 fungicide. 12-hr reentry.
  • Exotherm Termil at 1 can/1500 sq ft of greenhouse. It ignites to form a vapor that condenses back on the plants. See label for details. Group M5 fungicide. 24-hr reentry with no ventilation or 12-hr reentry with ventilation.
  • Hi Yield Captan 50 W Fungicide may be used in Oregon home gardens at 2 Tbsp/gal water. H
  • Nu-Cop 50 DF at 1 lb/100 gal water. Blooms may discolor. Group M1 fungicide. 24-hr reentry.
  • Mancozeb-based products can be used as mixing partners and provide some protection. Group M3 fungicides. 24-hr reentry.
    • Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker.
    • Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
  • Medallion WDG at 2 to 4 oz/100 gal water. Use with oils or adjuvants may damage plant. Group 12 fungicide. 12-hr reentry.
  • Mozart TR at 1 can/4,500 sq ft of greenhouse. Group 12 fungicide. 12-hr reentry with no ventilation.
  • OHP 6672 4.5 F at 10 to 14.5 fl oz/100 gal water plus another fungicide. Group 1 fungicide. 12-hr reentry.
  • Orkestra at 8 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
  • Pageant at 12 to 18 oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
  • Phyton 27 at 1.5 to 2.5 fl oz/10 gal water. Group M1 fungicide. 48-hr reentry.
  • Sil-Matrix at 1 to 4 quarts/100 gal water plus a nonionic surfactant. 4-hr reentry. O
  • Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
  • Terraguard SC at 4 to 8 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • Zyban WSB at 24 oz/100 gal water. Not to be confused with the smoking cessation drug. Group 1 + M3 fungicide. 24-hr reentry.

Some registered products offer only suppression of this disease and thus are not recommended for use. These products include Heritage.

Biological control

  • Prestop (Gliocladium catenulatum strain J1446) at 3.5 oz/5 gal water. Do not use with other products in the tank. 0-hr reentry. O

Reference Körner, O.and Holst N. 2005. Model based humidity control of Botrytis in greenhouse cultivation. Acta Hort. 691:141-148.