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Extension > Garden > Yard and Garden > Sirococcus blight of conifers

Sirococcus blight of conifers

Rebecca Koetter and Michelle Grabowski

Importance

North Central Research Station USDA FS, Bugwood.org

Fig. 1. Brown, wilted needles on red pine caused by Sirococcus blight.

Sirococcus blight of conifers is most prevalent on small landscape trees or on understory trees below infected mature-sized trees. Damage to large trees is confined to lower branches whereas infection can kill seedling aged trees. In Minnesota, Sirococcus blight only causes noticeable problems in years with consistently cool, wet weather.

Pathogen and susceptible plants

Sirococcus blight of conifers is caused by the fungus Sirrococcus conigenus. The disease affects several evergreen species but is most common on red pine (Pinus resinosa) and blue spruce (Picea pungens) trees in Minnesota. Other species that can be affected include ponderosa pine (Pinus ponderosa), white fir (Abies concolor), tamarack (Larix laricina), Norway spruce (Picea abies), white spruce (P. glauca), black spruce (P. mariana), red spruce (P. rubens), jack pine (P. banksiana), mugo pine (P. mugo), scots pine (P. sylvestris), and Douglas fir (Pseudotsuga menziesii).

Identification

Biology

The Sirococcus blight fungus overwinters in infected needles and shoots. During wet periods in spring and summer, when temperatures are 60-68° F, the spores spread through splashing or dripping water to start infections on young growing plant parts. Years with longer than normal wet periods have the most severe infections.

Infections occur on or next to the base of new needles and spread to shoots. Lesions eventually expand, killing the shoots. The infection may move into and kill one year old twigs. In a mature tree, infection is typically limited to the lower branches and does not significantly impact the health of the tree. Young trees can become severely disfigured by infection or killed.

Management

Always completely read and follow all instructions on the fungicide label.

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