Cause Unknown. Serbian spruce (Picea omorika) appears to sustain the most damage, but has been observed on a number of different spruce species and cultivars. Examinations of spruce, even before the bud cap has fallen off, have failed to find any signs of fungi, insects (which includes frass or exuvia) or eriophyid mites. Herbicide damage was suspected but the same degree of incidence was observed in treated vs. non-treated plots. The field pattern can be spotty but sometimes an entire block might show some effect. The problem is severe enough to make nursery-grown plants unsalable.
A similar fasciation has been reported in P. abies due to a phytoplasma but the symptoms are more typical of fasciations observed in other plants and not like the problem described here.
Symptoms The main symptom is a subtle to dramatic distortion and hardening of the needles. Shoots are stunted with needles closely pressed to one another like they were glued together. Shoots and/or needle bases may continue to expand while needle tips do not separate resulting in strange twists and turns of shoots and needle groups.
- Prune to remove the disfigured growth to retain marketability of affected plants.
Chemical control Until a specific cause is identified it is unwarranted to use fungicides or insecticides to try and control the problem.
Reference Kamińska, M., and Berniak, H. 2011. Detection and identification of three 'Candidatus Phytoplasma' species in Picea spp. trees in Poland. Journal of Phytopathology. 159:796-798.