Stem Lesions on Pine caused by Sirococcus conigenus

From: Dennis, J. 1990. Stem Lesions on Pine Caused by Sirococcus strobilinus. Seed and Seedling Extension Topics. Vol. 3, Number 2. p.1.

Most nursery personnel are familiar with Sirococcus blight which affects spruce and pine in both container and bareroot nurseries. It has been found rarely on 2+0 bareroot Douglas-fir seedlings and was recently found for the first time on western hemlock germinants. Sirococcus is seed-borne on spruce and affects container stock most seriously in the germinant stage. Under cool, wet, cloudy conditions, the fungus produces spores and spreads to the surrounding germinants. Infections at this stage kill the seedlings. Trees in the 2+0 stage are not fatally damaged but new growing tips that are infected are killed. A particularly susceptible stage is after bud break, during shoot elongation. This often coincides with moist weather and heavy spore release in the surrounding forests.

For two years both lodgepole and yellow pine seedlings affected by Sirococcus displayed different symptoms. The fungus appears to infect juvenile needles, travels down the needle, and produces a moist, purple lesion on the stem at the base of the needle. This lesion may be healed over leaving a small scar, or it can completely girdle the stem. Large scars create weak areas in the stem which make the seedlings unacceptable for planting. Stems with lesions break easily when handled or when under snow pressure. The main stem can be infected anywhere along it's length.

Laboratory culture tests at the Pacific Forestry Centre (PFC) on Sirococcus from stem lesions indicate that the B.C. Production Guide recommendations for Sirococcus blight should control the disease. However, preventing Sirococcus stem lesions has been difficult. This may be due to rain washing away sprayed material in open compounds or due to the difficulty in getting adequate fungicide spray penetration. Early detection and roguing affected material before the fungus produces spores and spreads to other seedlings is very important.

Sirococcus produces small, black fruiting structures which aid in identification. Care should be taken not to confuse them with fruiting bodies of other stem infecting fungi. Both Phoma and Sclerophoma produce black spore producing structures but these fungi are usually secondary to mechanical damage, drought stress or frost damage. They are good indicators of cultural or environmental stresses (and should not cause alarm). To prevent losses due to Sirococcus stem lesions, seedlings showing moist, purplish lesions, on succulent stem tissues should be sent to PFC for examination and identification.