Common Pests and Tree Health In The Saskatoon Area

Tree pests pose a significant challenge for urban forestry management in Saskatoon, where the city’s diverse canopy of native and planted species faces threats from both indigenous insects and introduced invasive species. The harsh prairie climate, characterized by long, cold winters and relatively short growing seasons, creates unique conditions that influence pest population dynamics and tree vulnerability. Common destructive insects such as the emerald ash borer, forest tent caterpillar, and aphid species can cause substantial damage to Saskatoon’s urban forest. It is affecting everything from residential boulevards lined with elm and ash trees to the established neighborhoods featuring mature poplar and birch.

Understanding the identification, life cycles, and management strategies for these prevalent pests is essential. For homeowners, arborists, and municipal staff working to maintain the health and longevity of Saskatoon’s urban canopy. It provides critical environmental benefits including air quality improvement, stormwater management, and urban heat island mitigation in this growing prairie city.

Aphids

These tiny insects measure roughly 2mm, are pear shaped, and are quite fragile. Usually these insects are a pale green colour, but occasionally can be a mix of colours. In Saskatoon, there are many types of aphids, which effect many different types of plants. The damage these insects do doesn’t typically have a negative impact on the plants health. They simply affect the leaf shape and size. Because they are harmless to plants, one shouldn’t be too quick using pesticides to be rid of them. If you do decide that they’ve become too big of a nuisance, there are specific products designed for aphid control.

Please read all labels carefully as using pesticides can have negative effects in other areas of your space. Another thing one can do if the aphids are a little much, is bring in lady bugs. This type of control is referred to as permaculture, and is a great, natural way to mitigate unwanted pests from your yard and home.

Ash Leaf Cone Roller

We observed this pest as new to the urban areas of Saskatoon and it effects ash trees primarily. This insect is a small brown moth, and it lays its eggs on the young leaves of ash trees. The small larvae feed between the upper and lower surfaces of the leaf, commonly known as leaf mining. When the larvae have used up the food from the nest leaf, they use silk threads and drift in the wind to knew leaves.

Once at the new leaf, they start rolling it into a cone, and after they are finished pupating, emerge as an adult moth. These adults usually appear in the summer, however, they put themselves in a state of sleep until the fall. Upon waking in the fall, they begin immediately to find a place to survive the winter, and reappear the following year. These moths, although called a pest, don’t do enough damage warrant preventative measures. If you stick to maintaining your trees health through proper watering and pruning, no harm will come from the Ash Leaf Cone Roller.

Cottony Ash Psyllid (CAP)

This pest is non native to Saskatoon and is affecting mancana and black ash trees throughout the city. These trees in particular are being hit the worst. The combination of drought and infestation is leading to a loss of these trees. The CAP are very small, green to yellow-green in colour, and are most easily recognized by the destruction they cause. They leave a white cotton residue curled within or along the length of the leaves. Heavy infestation leaves the tree partially defoliated, whatever greenery is left is twisted into a cauliflower or corkscrew shape.

In 2016, Saskatoon did its first study of this outbreak and found that Black Ash, Manchurian Ash and a mix between the two, often times called Northern Treasure and Northern Gem, are the types of trees being affected by the CAP. Other species of ash trees in Saskatoon such as Green, White, and Mountain Ash which aren’t to be impacted.

There is no quick an easy remedy for removing the cottony ash psyllid. What other cities across Canada have done has shown that chemical treatment only slows the loss of the trees. This city has made the decision to have all affected trees removed, taking down 1600 trees in 2018, and will be taking down 2100 and 800 of the remaining trees in 2019 and 2020 respectively.

If you’ve noticed any symptoms discussed above, please call your local arbourist (306-400-5425) or the city of Saskatoon to assess what condition your tree is in. Please try and act fast, as this pest moves along quite quickly.

Dutch Elm Disease

This fungal disease was brought to America in the 1930’s from the Netherlands, and has since wiped out millions of elm trees across North America. July of 2015 was the first confirmed report of Dutch Elm Disease in Saskatoon. Between the months of June and August are the best times to detect infected trees, with the symptoms showing in the leaves. They will start to yellow and wilt, and finally turn brown and curl before falling off completely.

The disease itself is spread by a few species of elm bark beetles. As these insects take flight in search of new elm trees to lay their eggs, infected tree fungus will attach spores to the bodies of the beetles who will then spread the illness to the new host tree. For this reason, the City of Saskatoon prohibits pruning of any elm tree during the months of April to September, while the beetles are most active. It’s encouraged to maintain your elm trees outside this period, as regular pruning encourages strong growth and inhibits the susceptibility of most disease all together.

Another note, the province of Saskatchewan prohibits the storing, transportation and use of all elm wood by products. The only exception to this law is in the transport to a designated landfill near you.

If you think your tree may have Dutch Elm Disease, don’t hesitate to call us, Saskatoon Tree Removal, or the City of Saskatoon to assess the situation.

Emerald Ash Borer

This pest is highly destructive. The insect in known to affect all types of ash trees, with the larvae of the emerald ash borer feeding beneath the bark. This pest is not currently in Saskatoon, although monitoring stations have been set up in many locations across the city. At the time of this writing, roughly 25% of all trees on the cities property are ash trees.

An outbreak of the emerald ash borer would be devastating, and being as they’re so hard to detect, the city of Saskatoon has multiple traps laid out and monitored regularly. This insect is able to spread through the transport of infected wood. Please be responsible when taking wood in and out of other municipalities, and always contact the department of forestry to find out if there are any restrictions on the transport of wood.

Forest Tent Caterpillar

The body of a forest tent caterpillar is dark, and has white spots running along the length of its back. They are roughly 5cm long once the larvae is fully matured, and has long hairs covering its body, know as setae. The caterpillars will start spinning cocoons in June, and a yellow, thick, furry bodied moth will appear shortly after.

While in the larvae stage, the forest tent caterpillar will feed on a large number on tree leaves, including chokecherry, ash and poplar. During heavy outbreak years, these pests have been know to completely defoliate trees. Although a full year of defoliation won’t usually harm a trees health, multiple years of back to back greenery loss can result in a decline of that particular tree.

Outbreaks can last for up to 7 years, but generally are between 2 to 4 years in length. During the worst of the years, it can seem like many trees are being harmed, but in reality, almost all of them are fine and won’t require any treatment. In large numbers, these insects would be considered a nuisance, but have no long lasting negative effect on our Saskatchewan trees.

You can help limit the number of these larvae developing in your yard by keeping a close eye on your affected trees come early spring. If you notice their white cocoons on any of the branches within reach, you can simply prune them off. It’s recommended to put the pruned branches and leaves in a garbage bag, and dispose of in your bin. Other ways to help mitigate leaf damage is to take the time to spray them off with water once they start emerging from the cocoon sacks. No sprays or pesticides are needed, this is a natural cycle.

Spider Mites

Are usually very small, less then 1mm in length, and are different then insects. They have only 2 body segments and have 4 pairs of legs, and typically attack fir, spruce, cedar and juniper trees. These pests feed on conifers, which leads to the needles or foliage to turn yellow and fall off.

They lay their eggs in the fall at the base of the needles, and hatch in the later spring months. Once hatched, the new brood will feed on the lower, inner most greenery which results in the most damage. At this time, the City of Saskatoon doesn’t have a control measure for dealing with spider mites, so if you suspect your tree has been infected contact your local arborist to assess the extent of the damage and to talk about options to control the problem.