Cause Uromyces dianthi, a fungus, has been reported from all three states of the PNW. Does not need the alternate host (Euphorbia spp.) to be a problem. Can be spread by importation of diseased nursery stock. The urediniospores can remain viable for 185 days. They are spread by wind, splashing water, or by infected cuttings. Germination is best at 50°F along with a film of water on the leaf surface that lasts for 9 to 12 hours. Spores enter leaves via stomata. The disease is favored by cool nights (60°F) alternating with warm humid days. Plants can be attacked at any stage of development and flower production and quality is reduced. Puccinia spp. can also occur on carnation but have not been reported from the PNW.
Symptoms Chocolate or cinnamon-brown pustules with powdery spores, up to 0.25 inch, break out on both sides of leaves and on buds and stems. Pustules are surrounded by a yellow margin. Uredinia (lighter brown) and telia (darker brown) may be scattered on plant parts or in groups. Leaves curl up and often die. Stems may be girdled when several pustules develop around a shoot. Plants become stunted and may not flower.
Cultural control
- Use culture-indexed plants free of the pathogen.
- Remove infected plant debris during production and thoroughly clean and sterilize the greenhouse between production cycles.
- Avoid overhead watering or any practice that keeps plants wet for extended periods.
- Space plants to allow good air circulation.
Chemical control Best used before symptoms develop.
- 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.
- Bonide Captan 50 WP may be used in home gardens at 1.5 Tbsp/gal water. H
- Eagle 20 EW at 6 to 12 fl oz/100 gal water. Group 3 fungicide 24-hr reentry.
- Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-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
- Propiconazole-based products. Group 3 fungicides.
- Banner MAXX at 5 to 8 fl oz/100 gal water. Not for use in the greenhouse. 12-hr reentry.
- Infuse Systemic Disease Control at 1 Tbsp/gal water. H
- 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.
- Tourney EZ at 1 to 4 oz/100 gal water. Group fungicide. 12-hr reentry.
- Ziram 76 DF at 1.5 to 2 lb/100 gal water. Group M3 fungicide. 48-hr reentry.
References Spencer, D.M., 1979. Carnation rust and its control by systemic fungicides. Plant Pathology 28:10-16.
Wolcan, S.M., Malbran, I., Mourelos, C.A., Sisterna, M.N., Gonzalez, M.P., Alippi, A.M., Nico, A., and Lori, G.A. 2018. Diseases of Carnation. In McGovern, R.J. and Elmer, W.H. (eds.) Handbook of Florists' Crops Diseases. Springer Int.