See:
Fir, True (Abies spp.) - Rusts
Cause The fungus Uredinopsis pteridis, which has true fir as its alternate host. Cool, moist springs favor disease development. Asciospores from firs can infect bracken fern any time in the growing season. Urediaspores occur on the fern, which can reinfect other bracken fern. Telia develop on the fern and overwinter in dead fronds. Teliospores germinate in spring and then infect other fir.
Symptoms Symptoms on fern are chlorotic markings on the upper surface and white pustules (uredinia) on the lower surface.
Cultural control Remove and destroy the alternate host if practical.
Chemical control Some products are labeled for nursery-produced "ferns" and can be used if not phytotoxic.
- Eagle 20 EW at 6 to 12 fl oz/100 gal water. Group 3 fungicide. 24-hr reentry.
- ProStar 70 WG at 3 to 6 oz/100 gal water. Group 7 fungicide. 12-hr reentry.
Reference Ziller, W.G. 1974. The Tree Rusts of Western Canada. Canadian Forestry Service Publication 1329.