See:
Pine (Pinus spp.) - Needle Rusts
Cause Many fungi have been reported on aster from the Pacific Northwest including Cercosporella virgaureae, Ovularia sp., Ramularia macrospora, Phyllosticta sp., and Septoria atropurpurea. Many of these fungi can overwinter in plant debris and are favored by conditions that keep leaves wet.
Rust has also been observed with Puccinia asteris and P. dioicae reported from all PNW states, P. magnoecia has been reported from Washington and P. extensicola from Idaho. The rust Coleosporium asterum has been reported from all PNW states and C. solidaginis has been reported from Washington (alternate hosts are generally pines).
Symptoms Septoria will produce brown spots on leaves, which may cause the leaf to die. Minute black dots (pycnidia) may be visible within the spots.
Coleosporium Rust - Bright-orange pustules (uredinia) develop on the leaves then become reddish-brown and crusty (telia). Defoliation may follow severe infections.
Cultural control
- Use clean seed.
- Remove and destroy infected plants or plant parts.
- Avoid sprinkler irrigation.
- Do not plant in wet areas.
Chemical control Use as foliar sprays before wet weather is expected.
- 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.
- 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.
- Medallion WDG at 1 to 2 oz/100 gal water as a foliar spray is registered to control several leaf spotting organisms. Use with oils or adjuvants may cause plant damage. Group 12 fungicide. 12-hr reentry.
- Ortho Rose & Flower Disease Control at 2 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.
- Spirato GHN at 1 to 2 fl oz/100 gal water. Use with oils or adjuvants may cause plant damage. Group 12 fungicide. 12-hr reentry.
- Ziram 76 DF at 1.5 to 2 lb/100 gal water. Group M3 fungicide. 48-hr reentry.
References Farr, D.F., Bills, G.F., Chamuris, G.P., and Rossman, A.Y. 1989. Fungi on plants and plant products in the United States. APS press.
Raabe, R.D., and Pyeatt, L. 1990. Control of rust of china aster and comments on the name of the pathogen. Journal of Environmental Horticulture 8:89-92.