Cause The fungi Sirococcus conigenus and Kabatina sp. have been associated with blighted needles of Altas (Cedrus atlantica) and Deodar (Cedrus deodara) cedars in both Oregon and Washington; however, Sirococcus is found most often. More of a problem in years with prolonged wet, cool springs. Infection is on or adjacent to needle bases on new shoots. The disease cycle is completed in 1 year, although spore dispersal from dead parts may continue an additional 10 months. The fungus overwinters in dead shoots. Conidia are dispersed by splashing water during the spring and summer, with peak dispersal during the period of host shoot growth. Temperatures of 60 to 70°F are most favorable for disease development. Symptoms appear about 2 weeks after infection, and lesion expansion on a given shoot may be completed after 4 to 6 weeks.
Symptoms Tan-pink needles are found in the spring. The blight may be only on the needles or extend through the new shoot into the previous year's growth. Terminal or lateral shoots may be blighted. Discolored tissue does not extend far into the branches. Shoot death and needle drop on established plants occur from June into August. Pycnidia develop on the bases of killed needles and along the stem of the killed shoot in late spring to early summer or the following spring. Similar symptoms have been seen without the association of any fungi.
Cultural control Remove and destroy blight plant material and plant debris that is found under trees or caught in limbs.
Chemical control No chemicals are specifically registered for this disease on cedar. However, according to IR-4 data, products that contain mancozeb, copper hydroxide or azoxystrobin are safe on these trees and may have some effect against this fungus. Use when new shoots are breaking bud and expanding.
- 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.
- Pentathlon DF at 1 to 2 lb/A or per 100 gal water.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
Reference Bronson, J.J., Stanosz, G.R., and Putnam, M.L. 2003. First report of Sirococcus conigenus on Deodar cedar in Oregon. Plant Disease 87:1006.