Sirococcus Shoot Blight
Seeds, Twig, Annual shoot, cones scale, bud scale, Needle
Common throughout the distribution range of red pine. The species is frequently found in temperate and boreal forests in North America and Europe.
Damage, symptoms and biology
The disease only kills annual shoots; hence the name shoot blight.
Climate plays a determining role in the development of outbreaks. During moist periods in the growing season, spores ooze out from the fruiting bodies and are dispersed by wind or rain splash, spreading the infection throughout the tree or to neighbouring trees. Symptoms may vary, depending on age and host species.
The fungus overwinters on dead needles, shoots and cone scales. The spores are spread in the spring of the following year and optimum dispersion occurs during shoot elongation. The tender, barely lignified young needles become infected as soon as they appear and in the early summer, when temperatures fluctuate between 16°C and 20°C. A small drop of resin can often be observed at the base of these needles. Infected shoots die within 4 to 6 weeks and the needles collapse at their base and bend sharply downward, producing a drooped, hooked appearance. The dead needles may stay on the tree for 2 to 3 years, and change in colour from reddish to a bleached-straw brown. The affected branches die because the terminal buds can no longer support new growth. The fungus can spread back along the twigs into the main stem and cause small purplish, elongated, sunken cankers. Soon after the shoots die in the spring, small fruiting bodies called pycniums form at the base of infected needles or under the bundle sheath, and on twigs, bud scales and cone scales. The pycniums, which are initially brown and later turn black, are found more often on spruce twigs, while on pine trees, they are more abundant on the needles.
Infected seeds become vectors of the disease. In nurseries, they cause significant damage during seed production. Seeds started in containers quickly die.
Infection is most common on the lower branches of trees but the disease can spread rapidly throughout the entire crown or through an entire plantation with intermingling crowns. Young, understory trees and trees in young plantations are very vulnerable to infection, and may be severely disfigured following repeated attacks and may die. Generally, the fungus only colonizes the lower branches of older and bigger trees; however, those trees may die after several years of successive severe attacks.
The removal of infected trees in and around nurseries or young plantations and windbreaks (which can also be an inoculum source) is strongly recommended, although this operation is not guaranteed to interrupt the cycle because the fungus persists on the twigs and cone scales. Infected trees should be removed during the dormant growing season to lessen the spread of the spores. In addition, measures aimed at promoting rapid drying of branches will minimize development of the disease.
In forest settings, the disease becomes a serious problem only in uneven-aged stands. Removing the infected understory in these stands will effectively reduce the incidence of the disease because young trees are especially vulnerable.
For ornamentals, infected shoots should be pruned off and removed by bud break in the early spring.
Fungicide treatment is only recommended and practical in forest nurseries as a preventive measure during the susceptibility period, which varies depending on the region, i.e. before and during the peak period of spore dispersion (16 °C–20 °C).
The curved terminal shoots can be confused with pine weevil, but there are no holes in the wood.
Recently, Sirococcus piceicola sp. nov. was defined on spruce and S. tsugae sp. nov. was defined on cedar and Western hemlock.
Canadian Forest Service Publications
Information on host(s)
Cedars, Douglas-fir, eastern white pine, Engelmann spruce, hemlocks, Jeffrey pine, lodgepole pine, mountain hemlock, mugho pine, ponderosa pine, scots pine, shore pine, Sitka spruce, tamarack, whitebark pine, white fir
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