Common pests & diseases

Tower Poplars

Tower Poplars have been at great risk over the last few years as Bronze Leaf Disease moved into our province. Bronze leaf disease is caused by the fungus Apioplagiostoma populi and affects mainly Swedish columnar aspen and tower poplar trees. Symptoms occur in late summer and early fall when leaves rapidly turn bronze or chocolate brown. Veins remain bright green and eventually turn to black. Fungal diseases spread through spores attached to animals, like a bird landing on an infested tree and then flying to your tree.  

Black Knot Disease

Black Knot Disease is a widespread fungal disease that attacks plum and cherry trees, most commonly seen in the Shubert chokecherry in Saskatoon. Once established black knot is easily identified with its hard, uneven, black galls that surround twigs and branches. Black knot is controlled by pruning early in its infection of a tree. Once the disease has spread, it moves into the trunk wood of the tree and at that point, the only course of action is removal.  

Cottony Ash Psyllid

Cottony Ash Psyllid is a pest affecting black ash trees in Saskatoon. It is most commonly diagnosed by the damage it does to black ash trees, including loss of foliage, white residue on leaves, and curling leaves into a “cauliflower” like shape. There are only a few treatments for this pest, and in Saskatoon the widespread damage it caused left the city little choice but to fully remove infested trees.  

Needle cast

Needle cast is a disease often spotted in our city that turns areas on branches of Spruce trees purplish brown. Trees that are stressed by drought are easily affected by this. The most commonly affected tree is the Colorado Blue Spruce, however, it has been seen in White Spruce as well.    

Fire Blight

Fire Blight is a contagious bacterial disease affecting trees in the Apple and Pear family. It causes severe blighting of blossoms, shoots, limbs, and fruit. Containing the spread of Fire Blight is done by pruning during the months the tree is in dormancy, as well as taking precautions to disinfect pruning equipment for each cut made on the tree.  

Dutch Elm Disease

Dutch Elm Disease is a vascular disease affecting Elm trees. It is caused by two closely related species of fungi, both of which are transmitted by elm bark beetles, root grafts, and pruning tools. It blocks water movement and eventually leads to the death of the entire tree. Prevention of Dutch Elm Disease is very important in Saskatoon as we have an estimated 100,000 Elms in our city.  

Ways to prevent Dutch Elm Disease:  

• Do not store or transport elmwood – Provincial regulations prohibit the storing or transporting of elmwood. Elmwood must be disposed of at the City landfill. 

• Do not prune elm trees during the provincial elm pruning ban from April 1 to August 31. 

• Remove dead and dying tree limbs promptly as they are a breeding site for beetles that can act as a vector. 

• Sanitize tools after working on elm trees. 

• Keep elm trees healthy and rapidly remove infected trees.