Cause Sirococcus conigenus (formerly Ascochyta piniperda), a fungus. It attacks many conifer including western hemlock; Jeffery, ponderosa, and red pine; and blue and sitka spruce. The fungus overwinters in dead shoots. Spores are rain-splashed from one tree or seedling to another. Infection is on or near the base of needles on new shoots as they begin to grow in the spring. Seedling infestation occurs when the fungus colonizes the seed cones.
Symptoms New shoots die back in summer. At first, needles may turn brown starting at the base or fall off in the middle of the shoot near the infection point. If the twig dies during shoot elongation, a characteristic hook shape develops. Diseased twigs slowly die back to the branch where the bud began. Numerous small, black, fruiting bodies (pycnidia) develop on the twig about a year after the infection began. Can be confused with frost or herbicide damage.
- Prune out affected branches if practical and remove plant debris that is found under trees or caught in limbs.
- Avoid overhead irrigation, or water such that plants are not wet for extended periods of time.
- Keep seed lots separate when growing seedlings.
- Closely inspect new seedlings; remove any that show signs of infection.
- Fertilization with magnesite compounds have been helpful to reduce disease severity when magnesium has been limiting.
Chemical control Start applications at bud break, 2 weeks apart when wet weather is expected.
- Bravo Weather Stik at 2 to 3.5 pints/A. Group M5 fungicide. 12-hr reentry.
- Echo 720 at 2 to 3.5 pints/A. Group M5 fungicide. 12-hr reentry.
- Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-hr reentry.
- Mural at 4 to 7 oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
Reference Sinclair, W.A. and Lyon, H.H. 2005. Diseases of Trees and Shrubs. Second Edition. Ithaca, NY: Cornell University Press.