Spruce Needle Casts and Blights

Lirula macrospora (Hartig) Darker 
Lophodermium piceae (Fuckel) Hӧhn 
Rhizosphaera pini (Corda) Maubl. or Rhizosphaera kalkhoffii Bubák 

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

Current Status & Distribution in Alaska (2023 update)

Three fungi that cause needle casts and blights of spruce occur throughout much of Alaska (Detection Maps), although they are rarely noticeable. Lirula needle blight, more common in coastal forests, was found on Sitka spruce at 13 sites across Southeast Alaska this year. Discoloration symptoms observed on one-year-old Sitka spruce needles in the northern Panhandle were less common and severe compared to the past two years. In Interior and Southcentral Alaska, L. macrospora was found on white and black spruce at five locations between Healy and Donnelly north of the Alaska Range, and on one white spruce near Anchorage. Rhizosphaera needle cast symptoms became apparent on Sitka spruce in Southeast Alaska in Fall 2023. Due to late symptom onset, just seven ground observations were made in Gustavus, in Juneau, and on Kupreanof Island. Infected needles collected on Kupreanof Island had fruiting structures containing spores, providing an opportunity to measure spores to verify the identity of the causal fungus. The spore sizes observed (6-7 µm x 3-5 µm) fall within the range expected for Rhizosphaera kalkhoffii rather than R. pini, as we have long referred to this pathogen in Alaska. This species verification work will continue. In Southcentral Alaska, three observations were recorded near Anchorage. In the Interior, three observations were made on white spruce near Healy. Lophodermium needle cast was observed at one location on Prince of Wales Island in Southeast Alaska. 

Photos

Scroll through these Flickr albums of Lirula macrospora, Lophodermium piceae, and Rhizosphaera pini/Rhizosphaera kalkhoffii from Alaska Forest Health Protection, Forest Service, Alaska Region.

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 one-year-old needles, and tan two-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 sp. 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 needle cast 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