See:
Cedar, Western Red (Thuja plicata) - Leaf Blight (Keithia Blight)
Pine (Pinus spp.) - Lophodermium Needle Cast
Cause Several fungi have been found by the OSU Plant Clinic on blighted leaves of juniper. Wet weather and poor air circulation, which keep foliage wet, favor disease development. Lophodermium juniperinum has been found many times over the years. Although this fungus is found as a secondary problem, it may be primary under certain conditions. This fungal genus is more familiar as a problem on pines. Didymascella (likely D. tetramicrospora) was found on several samples in the early 1970's. This fungus genus is more common on western red cedar and was called Keithia blight based on the old name of the pathogen.
Symptoms Lophodermium juniperinum forms small, shiny, black elliptical fruiting bodies on the leaves.
Cultural control
- Prune out and burn affected twigs and branches.
- Avoid overhead irrigation or apply such that plants are not wet for extended periods of time.
- Do not over-fertilize.
- Space plants for good air circulation.
- Select cuttings only from disease-free stock plants.
Chemical control The chemicals used for twig blight might be helpful to manage these foliar problems.
- Cleary's 3336 EG at 16 to 24 oz/100 gal water. Group 1 fungicide. 12-hr reentry.
- CuPRO 5000 at 1.5 to 5 lb/A but only up to 2 lb/A when new growth is present. Group M1 fungicide. 48-hr reentry.
- Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-hr reentry.
- Kocide 3000 at 0.75 to 1.75 lb/A. Group M1 fungicide. 48-hr reentry. O
- Mancozeb-based products can be used as mixing partners and provide some protection. 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.
- Mural at 4 to 7 oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- Phyton 27 at 1.3 to 2.5 oz/10 gal water. Group M1 fungicide. 48-hr reentry.
- Propiconazole-based products. Group 3 fungicides.
- Banner MAXX at 5 to 8 fl oz/100 gal water. 12-hr reentry.
- Infuse Systemic Disease Control at 1 Tbsp/gal water. H
- ProCon-Z at 5 to 8 oz/100 gal water. 24-hr reentry.
- Tourney EZ at 1 to 4 oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Reference Pantidou, M. E. and Darker, G. D. 1963. The species of Didymascella on Juniperus. Mycologia, 55:415-420.
Smith Jr, R. S. and Scharpf, R. F. 1993. Needle diseases. Diseases of Pacific Coast Conifers, 521, pp.33-60.