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Cause Puccinia chrysanthemi (formerly P. tanaceti), a fungus that overwinters on vagrant plants or plant residue. There is no alternate host so spores produced on chrysanthemum will reinfect the plant. Free moisture is necessary for infection. Optimum temperature for disease expression is 59°F to 70°F. Temperatures greater than 100°F for 8 hours will kill infections.
Symptoms Pale yellow flecks are first observed on both leaf surfaces. Small blister-like bodies (uredinia) that develop on leaves' undersides later break open to expose a reddish brown, powdery mass of spores. Uredinia are often found in concentric rings. Symptoms may be very subtle on the upper leaf surface. Stem infections have not been observed. Affected plants may be stunted and produce few flowers. Early symptoms are similar to white rust.
Cultural control
- Keep susceptible cultivars isolated.
- Pick off and burn affected leaves.
- Use cuttings from healthy plants only.
- Remove plant debris and escaped plants.
- Keep humidity low, and avoid wetting foliage. Use drip irrigation.
- Exposure to temperatures over 87°F for 24 hours can cure infections that are several days old.
Chemical control
- 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.
- Banner MAXX at 8 to 12 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
- Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water. Group M5 fungicide. H
- Broadform at 4 to 8 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- Compass 50 WDG at 2 to 4 oz/100 gal water. Group 11 fungicide. 12-hr reentry.
- Daconil Weather Stik at 1.38 pints/100 gal water. Group M5 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.
- Mancozeb-based products. 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.
- 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.
- 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.
- Postiva at 10 to 28 fl oz/100 gal water. Group 3 + 7 fungicide. 12-hr reentry.
- ProStar 70 WG at 3 to 6 oz/100 gal water. Group 7 fungicide. 12-hr reentry.
- Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 1 fl oz/gal water. Group 3 fungicide. H
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
- Sulfur (90%) at 3 Tbsp/gal water. Avoid using sulfur during hot periods or on open flowers because it may cause bleaching. 24-hr reentry. H O
- Terraguard SC at 2 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.
- Ziram 76 DF at 1.5 to 2 lb/100 gal water. Group M3 fungicide. 48-hr reentry.
References Demers, J.E., Crouch, J.A., and Castlebury, L.A. 2015. A Multiplex Real-Time PCR Assay for the Detection of Puccinia horiana and P. chrysanthemi on Chrysanthemum. Plant Disease 99:195-200.
Punithalingam, E. 1968. Puccinia chrysanthemi. CMI Descriptions of Pathogenic Fungi and Bacteria, No. 175. Surrey, England: Commonwealth Mycological Institute.