Forest & Grassland Health

Spruce Needle Casts and Blights

Rhizosphaera needle blight on Sitka spruce.

Rhizosphaera needle blight of Sitka spruce near Juneau in 2019.

 

Rhizosphaera pini (Corda) Maubl.
Lirula macrospora (Hartig) Darker
Lophodermium piceae (Fuckel) v. Hӧhn

Host(s) in Alaska:

Sitka spruce (Picea sitchensis)
white spruce (P. glauca)
black spruce (P. mariana)
Lutz spruce (P. glauca x P. sitchensis)

Habitat(s): spruce needles

Photos

Click on image for larger version.

Rhizosphaera needle discoloration in the lower and interior crown of Sitka spruce.

Rhizosphaera pini causes needle discoloration of the lower and interior crown of Sitka spruce.

Discoloration of older Sitka spruce needles caused by Rhizosphaera pini.

Discoloration of older Sitka spruce needles caused by Rhizosphaera pini.

Discoloration and casting of older Sitka spruce needles caused by Rhizosphaera pini

Discoloration and casting of older Sitka spruce needles caused by Rhizosphaera pini.

Spherical black fruiting structures of Rhizosphaera pini emerge from stomata.

Spherical black fruiting structures of Rhizosphaera pini emerge from stomata.

Spherical black fruiting structures of Rhizosphaera pini emerge from stomata.

Spherical black fruiting structures of Rhizosphaera pini emerge from stomata.

Needle discoloration symptoms caused by Lirula macrospora.

Needle discoloration symptoms caused by Lirula macrospora.

Long black fruiting structures of Lirula macrospora on Sitka spruce needles.

Long black fruiting structures of Lirula macrospora on Sitka spruce needles.

Long black fruiting structures of Lirula macrospora on Sitka spruce needles.

Long black fruiting structures of Lirula macrospora on Sitka spruce needles.

Sitka spruce needles with zone lines and fruiting structures of Lophodermium piceae.

Lophodermium piceae fruiting structures and black zone lines on Sitka spruce needles.

Fruiting structures of Lophodermium piceae.

Lophodermium piceae fruiting structures on a Sitka spruce needle.

Current Status & Distribution in Alaska (2020 update)

Three fungi cause needle blight or needle cast of spruce throughout much of Alaska (see Distribution Map). Rhizosphaera needle blight damage of Sitka spruce near Juneau was elevated in 2019 but returned to normal levels in 2020. Lirula needle blight was the most dominant spruce needle blight detected in 2020. Lophodermium needle cast is another common but minor foliage disease of spruce in Alaska. 

Symptoms, Biology & Impacts

These diseases can be distinguished based on the fungal fruiting structures on needles, and (when severe) also on the pattern of foliage discoloration. Symptoms are often most severe in the lower and interior tree crown, where persistent needle wetness promotes foliage disease. Rhizosphaera and Lirula needle casts are considered more damaging than Lophodermium needle cast in Alaska.

Lirula: Fruiting structures are black and elongated on the undersides of needles. Spores are released from mature fruiting structures on infected two-year-old needles in spring to infect newly emerging foliage during shoot elongation. Red-brown foliage discoloration symptoms become apparent one year after infection, with needles turning tan-brown after two years. This results in a distinctive pattern of green new growth, red-brown 1 -year-old needles, and tan 2-year-old needles, often interspersed with healthy foliage. Although usually not necessary, chemical control is effective when applied around bud break. Thinning and pruning trees to increase air movement in the crown can reduce infection. Smaller trees are often more severely affected than large trees.

Lophodermium: Fruiting structures are black and elliptical, often with black zone lines crossing needles. Symptoms generally appear in older groups of adjacent needles. Damage may be more common on large trees compared to smaller trees in young-growth stands.

Rhizosphaera: Small black fruiting structures occupy pores for gas exchange (stomata) on needles (generally requires a hand lens for identification). Spores are rain-splash dispersed from fruiting bodies in spring (and summer if conditions are suitable), primarily infecting new needles. Red-brown foliage discoloration and premature needle shed symptoms become apparent in late summer and fall, 1.5 years after infection. Severely defoliated trees can lose nearly all of their >1-year-old needles, but associated tree mortality is rare. Outbreaks may develop when temperature and moisture conditions are favorable for dispersal and infection for multiple consecutive years.

Historic Activity

Between 1972 and 1984, spruce needle cast caused by Lophodermium piceae was the only spruce needle cast pathogen implicated in annual Forest Health Conditions in Alaska reports. It was said to be common in Southeast Alaska (1972), and noticeable north of Icy Bay and on the Kenai Peninsula, especially Homer (1982-1984).

From 1985 to 1991, spruce needle cast caused by Lirula macrospora occurred at moderate to high levels in coastal Alaska, prompting study of spore dispersal and symptom development (Hennon 1990). This disease was considered the most damaging of the three needle cast diseases. Elevated disease levels were noted on Sitka spruce in Southeast Alaska, white and Lutz spruce on the Kenai Peninsula and north of Anchorage, and Sitka spruce on Kodiak Island. In 1991, a fungicide study demonstrated that chemical control was effective when applied soon after bud break (though chemical control is not usually warranted). It was observed that disease is often most severe in stands in which spruce grows with red alder, perhaps due to soil nutrition. Lirula also caused moderate damage in 1994 (coastal Alaska), 1997 (Afognak Island across an estimated several thousand acres; at moderate to high levels in most areas in the range of Sitka spruce). In 2015 and 2016, damage from Lirula was noted at several locations in coastal Alaska (e.g., near Juneau, Kake and on the Kenai Peninsula). 

Needle cast caused by Rhizosphaera pini was observed on Sitka spruce throughout Girdwood, Twenty-mile and Portage Valleys south of Anchorage in 1992, but was thought to cause negligible damage in natural forest settings (problematic in nurseries and plantations; offsite plantings). However, in 1993-1994, Rhizosphaera occurred at damaging levels in coastal Alaska, killing lower and inner crowns of Sitka spruce near Juneau. Rhizosphaera returned to endemic levels until 2009, when it became epidemic on Sitka spruce for one year in many areas of Southeast Alaska: “the largest and most intense outbreak in memory.” Elevated disease levels were also observed from 2013 to 2015. Forest Health Protection is hoping to confirm the species identity of Rhizosphaera in Alaska, which may be R. pini or R. kalkhoffii.

Survey Method

Detection of spruce needle cast diseases is usually based on informal ground-assessments and permanent monitoring plots. Fall symptom development and lower crown symptoms preclude consistent detection during aerial survey.

Detection Map

Click map image for larger version.

Observed locations of spruce needle casts and blights in Alaska as of 2020.

Georeferenced observations of Lirula macrospora, Lophodermium piceae and Rhizosphaera pini in Alaska as of 2019 with the modeled distribution of spruce (Piceae spp.) hosts. Observations without georeferenced datapoints are excluded, but are described in the Historic Activity section above. Host tree distributions were developed by the Forest Health Technology Enterprise Team in 2011 (240-m resolution, based on dominant tree cover by diameter).

 

Links to Resources & Publications

Hennon, P. E. 1990. Sporulation of Lirula macrospora and Symptom Development on Sitka Spruce in Southeast Alaska. Plant Disease 74:316-319. Available here.

Juzwik, J.; O Brien, J. G. 1990. Premature Needle Loss of Spruce. NA-PR-01. [Radnor, PA]: U.S. Dept. of Agriculture, Forest Service, Northern Area State & Private Forestry. Available here.

Forest Health Leaflet R10-TP-12 on Spruce Needle Cast (Lirula macrospora)

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife-if they are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended practices for disposal of surplus pesticides and pesticide containers. Mention of a pesticide in this publication does not constitute a recommendation for use by the USDA, nor does it imply registration of a product under the Federal Insecticide, Fungicide, and Rodenticide Act, as amended. Mention of a proprietary product does not constitute an endorsement by the USDA.

 

Content prepared by Robin Mulvey, Forest Pathologist, Forest Health Protection, robin.mulvey@usda.gov.

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