Incidence and Impact of Swiss Needle Cast in Forest Plantations of Douglas-fir in Coastal Oregon

Abstract

An epidemic of Swiss needle cast, caused by the ascomycete Phaeocryptopus gaeumannii, is causing defoliation and growth reductions in Douglas-fir forest plantations along the Oregon Coast. The area of symptomatic plantations has been monitored annually since 1996 by aerial survey; in spring 1999, 119,500 ha were affected. Pathogen and symptom development have also been monitored on nine permanent plots in stands of differing disease severity. Infection levels and symptom severity are greatest in low elevation plantations close to the coast. In areas of severe disease, trees retain only current year needles. Defoliation is proportional to the number of stomata occluded by pseudothecia of the fungus, with needles being shed when about 50% of stomata are occupied, regardless of needle age. Fungus sporulation and premature needle abscission are greatest on the upper branches of trees. Annual application of fungicides increases needle retention significantly. Tree height and diameter growth and total tree volume are reduced by disease, and tree volume is significantly correlated with needle retention on our plot trees. The epidemic continues to be most severe in Douglas-fir plantations established on sites where Sitka spruce and western hemlock or red alder predominated in earlier times.

Response of Douglas-fir leaf area index and litterfall dynamics to Swiss needle cast in north coastal Oregon, USA

“…However, plots with higher level of foliage retention tended to have a greater proportion of foliage in their litterfall because crown recession (branch mortality) was slower than on plots with low foliage retention [65]. Fogel and Hunt [15] reported that total litterfall wasspring when spores are released from pseudothecia in the stomates of older infected needles and are carried by wind and rain to newly emerged needles [21]. The spores germinate on the surface of a new needle, enter through the stomates, and grow in the intercellular spaces of the leaf tissue until pseudothecia begin to appear in the fall [21].…”

“…Fogel and Hunt [15] reported that total litterfall wasspring when spores are released from pseudothecia in the stomates of older infected needles and are carried by wind and rain to newly emerged needles [21]. The spores germinate on the surface of a new needle, enter through the stomates, and grow in the intercellular spaces of the leaf tissue until pseudothecia begin to appear in the fall [21]. Needles are shed when about 50% of stomata are occluded by pseudothecia [21].…”

“…The spores germinate on the surface of a new needle, enter through the stomates, and grow in the intercellular spaces of the leaf tissue until pseudothecia begin to appear in the fall [21]. Needles are shed when about 50% of stomata are occluded by pseudothecia [21]. The level of occlusion generally peaks in the late spring and early summer, so coincides with the secondary peak in foliage litterfall for stands with severe SNC.…”

Influence of Bravo fungicide applications on wood density and moisture content of Swiss needle cast affected Douglas-fir trees

“…More recently, this foliar disease has intensified in older, naturally established stands as well. Whereas effects on growth (Hansen et al, 2000;Maguire et al, 2002) and physiology (Manter et al, 2000) have been reported, there is very little information available about its effect on wood properties. Anecdotal observations suggest that SNC increases the proportion of latewood relative to earlywood; this shift in early/latewood proportion would be a logical outcome given that previous experimental work has demonstrated that the earlywood production is mostly dependent on old foliage and the latewood mostly on the new foliage (Onaka, 1950).…”

“…The pseudothecia emerge through the stomates and release spores in the spring and early summer. The amount of fungus and number of pseudothecia increase with age of the needle until the needle is dropped (Hansen et al, 2000). In heavily infected stands, first-year needles become chlorotic the following spring and drop from the tree during the second growing season.…”