Christmas Trees: Traditions, Production, and Diseases

Although the etiology is unknown, studies have shown that shading trees or foliar applications of calcium chloride during shoot elongation significantly reduce the incidence of symptomatic needles (Chastagner et al 1990c). These studies suggest that calcium deficiency may in part contribute to this disease. Although foliar applications of calcium chloride are effective in reducing the incidence of this disorder on both noble and grand fir, this treatment cannot be recommended as a management tool because of phytotoxicity associated with the rates and frequent number of applications required to reduce disease levels.

Grafted tree with symptoms
on the scion branches and
no symptoms on the
rootstock branches.
(Click on image for more detail.)

There is increasing evidence from the PNW and Denmark that the development of CSNN is under strong genetic control. In Denmark, Nielsen (personal communication) has found that noble fir provenances from Oregon and Washington were much more prone to CSNN than highly selected Danish provenances.

Seed from noble fir trees in the Riley/Fanno area of coastal Oregon have been shown to consistently produce high quality Christmas trees over a range of sites in the PNW (Brown, 1990, Brown and Landgren, 1995, Douglas, 1984 & 1991 and Landgren, 1999). Recent research has shown that there is considerable variation in the development of CSNN on different families of trees from this seed source (Chastagner and Landgren 1998). The fact that there was a significant correlation between the percentage of unmarketable progeny trees due to CSNN and the CSNN ratings of the mother trees, indicates that it should be possible to breed for trees with resistance to CSNN.

There has been some speculation that the limited susceptibility of the Danish provenances is somehow related to their dark blue coloration. This appears to be unlikely since the highly susceptible Riley/Fanno parents in the seed orchard also exhibited mature dark blue foliage characteristics similar to that which is associated with the highly selected Danish provenances.

Click image for more detail.

Very little information is currently available regarding the effect of cultural practices with respect to this disorder. Data collected during a 7 year long fertilization study indicates that fertilization with Urea-Sul or Sul-Po-Mag did not affect the level of CSNN which develop on the noble fir Christmas trees in these studies (Chastagner and Landgren 1998).