In Calgary, black knot fungus affects Mayday and Chokecherry trees. To manage black knot fungus, it’s essential to prune off infected branches 2 to 4 inches below each “knot” and dispose of them in a land fill. The fungus spores overwinter in the masses and reproduce in the spring. Pruning should be conducted when plants are dormant. The best time is during late winter when the abnormal “knotty” growths are clearly visible. The fungus is transported through air which carries the spores to new host. Fungal growth eventually chokes out the branch and kills it.
Bronze leaf is an air borne fungal disease that infects Swedish columnar aspens and tower poplars in Calgary areas. Symptoms of bronze leaf disease typically appear in late summer or early fall and may only be on a few branches or leaves. Infected leaves become dark reddish-brown, chocolate brown or bronze although the veins and the leaf stem may remain green for some time. Infected leaves remain on the tree throughout winter.
The fungus usually infects trees that are weakened by environmental stress, such as drought and freezing shock. Infection usually does not begin until trees are at least 10-15 years old.
The fungus generally enters through wounds. The infection usually starts on the lower branches and spreads upwards as spores of the fungus are dispersed by rain-splash. Needles on infected branches first turn purple and then brown and drop, leaving the infected branches bare. Cankered branches are usually covered with white resin.
This is commonly seen in stressed trees. As infected wood begins to die it often appears orange and may weep a brown liquid. Once the canker has gone completely around a stem, the rest of the stem quickly dies.
Scab may occur on leaves, fruit, stems and green twigs but infections of the leaves and fruit are most common and obvious.
Infection on leaves first appears on the lower side. Young lesions are velvety brown to olive green with indistinct margins and later turn dark brown to black. Lesions on older leaves are typically raised, dark green to gray-brown with distinct margins, and cause cupping on the underside of the leaf. Leaves that are heavily infected with scab will curl, shrivel and fall from the tree. On fruits, small black spots develop at first and later become brown, corky and scabby. Heavily infected fruit becomes deformed and cracked when infected at an immature stage.
Cedar-hawthorn rust occurs on cedar, juniper, apple and crab apple, hawthorns etc. In order to survive, the fungus generally moves from one type of host to another (for instance, from juniper to hawthorn).
Small yellow spots first appear after infection in the spring. As the spots mature and enlarge, they take on an orange color and develop tiny black dots in the center of the lesion. By mid-summer, tubes are visible on the undersides of mature leaf lesions or within the lesions on fruit, petioles or twigs infections. With severe rust, hawthorn foliage may turn bright yellow and drop prematurely.
The common symptoms of needle cast include brownish purple discoloration and eventual death of older needles, while current-year needles show no symptoms. Needle cast diseases of spruce are treatable. Within a few years after treatment, an infested spruce tree can look beautiful again.
Fire blight is one of the most destructive diseases of apple and pear trees. In Calgary, mountain ash, hawthorn and cotoneaster are also affected by blight. The bacteria can kill flowers, twigs and branches, and sometimes whole trees and shrubs. Mountain ash trees are badly affected by bacteria in Calgary and surrounding areas.
In spring, branch and trunk canker symptoms can appear as soon as trees begin active growth. The first sign is watery, light tan bacterial ooze that exudes from on branches, twigs, or trunks. The ooze turns dark after exposure to air, leaving streaks on branches or trunks.