Problem type: Disease
Name of problem: Sirococcus shoot (tip) blight
Plant name(s): Spruce (Colorado blue, black, white, Norway, red) and pine (red, Scots, mugo, jack)
Symptoms / Characteristics:
Browning, curling and wilting of young needles and succulent shoots are typical symptoms associated with Sirococcus shoot blight. Symptoms commonly (but not always) appear in the lower branches. In early summer, discolouration begins at the base of the needles and spreads until the needles are completely brown. Tiny drops of liquid may ooze from the base of symptomatic needles. A close examination of dead needles and shoots will reveal the presence of small, black dots, which are the fungal fruiting bodies. Infected shoots have a hooked appearance and eventually become defoliated. In some cases, senesced needles remain on the tree for a number of years before dropping. Small, purplish cankers form on current-year shoots. Repeated infections lead to lower branch dieback but plant death is uncommon in mature trees. Conifer seedlings rarely survive the disease.
Sirococcus shoot blight is caused by Sirococcus conigenus (formerly known as Sirococcus strobilinus). The fungus overwinters on infected plant debris. Cool and rainy spring conditions facilitate the spread of the disease onto newly formed conifer shoots. Once the fungus colonizes a host plant, subsequent infections of healthy trees can occur via rain splash or irrigation. The pathogen targets current-year or one-year-old growth but seldom invades older wood. In 2003, the disease was of particular concern in Winnipeg, MB, causing severe infections of Colorado blue and white spruce as well as Scots and mugo pine
Control / Preventions:
Remove and destroy infected shoots and needles on a regular basis in order to reduce potential inoculum sources and overwintering sites. This is especially important if nearby and understory plants are also susceptible to the disease, as fungal spores spread to healthy plants via rain splash or irrigation. In severe cases, the removal of infected overstory trees may be a necessary means of prevention. Shade conditions also facilitate the infection process. Ensure adequate spacing between susceptible trees in order to avoid high moisture, shade conditions that facilitate the spread of the disease. Registered fungicides are available and will most effectively control the disease if applied in late spring when the fungal spores initially spread to healthy host trees. Spray frequency may be increased during periods of rapid shoot growth and if high moisture conditions persist.