Pest Management

Parks Division
Tel: (306) 786-1780
Fax: (306) 782-2606

Tree Worms

Tree worms are a common pest within the City of Yorkton. There are two distinct species of tree worms that are prevalent in the city: the Forest Tent Caterpillar and the Cankerworm. Both species cause similar unsightly and unhealthy effects on trees, and can be controlled in the same manner.

Forest Tent Caterpillar adults are tan colored moths, with two thin dark, parallel oblique lines of one single, broad, dark band crossing the middle of the front wings. The mature larvae are 45-55mm long and are bluish to brownish in colour with diamond-shaped white spots on the middle of the back of each segment. It has two thin prominent broken yellow lines that extend along each side of its hairy body.

Both Spring and Fall Cankerworms are about 2.5cm long when fully grown. They range in colour from light green to brownish green with a dark stripe down the back.

Forest tent caterpillar larvae feed initially on the opening buds, later consuming parts of or whole leaves of broad-leaved deciduous trees and shrubs. During high populations, forest tent caterpillars can completely strip trees and will then feed on the understory shrubs and other vegetation.

Cankerworms leave small holes in the new leaves. As the cankerworm larvae eats, the holes become larger until only the leaf veins remain. During high populations, cankerworms can also completely strip trees of their leaves.

Will the tree be damaged?

Healthy trees should grow back their leaves 2-3 weeks after defoliations, or by early July depending on the year. However, their growth is slower and they are less able to fight potential new diseases and other insect attacks.


On smaller trees and shrubs, an effective means of controlling the forest tent caterpillar is pruning or breaking off the egg masses on the twigs and disposing of them in the garbage. This is best done in fall or in early spring when there are no leaves on the trees and the egg masses are most visable. After hatching, young colonies of larvae can be pruned off or squashed while they are resting in clusters on the main stem, especially in the evenings or on cool nights.

The best way you can control adult cankerworms is to band your trees before larval cankerworms become a problem. Banding your trees with a product such as Tanglefoot is an environmentally acceptable way to keep adult cankerworms from climbing the tree to lay eggs. You should band your trees by mid-March to control the spring cankerworm and by mid-septenber (or before the first hard frost) to control the fall cankerworm. Encourage your neighbours to also band their trees because cankerworms can travel on their silken threads as larvae. Remember to remove the band by the end of June to prevent rotting bark.

When trees are too large or there are numerous larvae of either worm species, a non-chemical insecticide that contains Bacillus thuringiensis var, kurstaki (BTK) such as Bioprotec ECO and Safer's BTKBiological Larvicide are good environmentally friendly ways to control tree worms. Chemical agents can also be sprayed to control worms. Remember to always follow the manufacturer's label when using chemicals. All Pest Control products purchased and used must be registered with Health Canada and contain a Pest Control Product (P.C.P. or PCP) Number on their label.

What is the City doing?
The City of Yorkton has a tree worm control program in place. At the first sighting of tree works, the Parks Division begins preparations for spraying City owned trees. Initial spraying uses a product called Dipel, which contains BTK. This product must be ingested, and is sprayed onto the leaves when the worms are feeding. During heavy infestations, a second spraying of a chemical insecticide called Pounce may be used, which begins working on contact with the worm.

City of Yorkton Tree Worm Control Program for 2017

Mosquito Control

The Culex Tarsalis species of mosquito is known to be the highest potential risk of transmitting the West Nile Virus. The Culx Tarsalis seems to be most active in the mid to late summer months; however, protection should be ongoing.

Femail mosquitoes bit for a blood meal which allows them to lay eggs. Eggs may stay dormant for years. When there is sufficient water the eggs will hatch, continuing the cycle of mosquitoes. Large bodies of water such as Jaycee Beach or the Ravine Ecological Preserve do not have a lot of mosquitoes as the water is too deep. Eggs are lain in shallo areas of standing water.

City crews will be out "dipping" standing water sites looking for second and third star stage larvae. Once mosquitoes have reached the pupae stage, they cannot be treated. If larvae are present, the water site will be treated with Vectobac (biological friendly), and they area will be signed. Mosquito control signs may remain up for the season.

The City will be monitored throughout the summer and water sites treated accordingly. The City will have detailed mapping of the mosquito sites that have standing water, those that have been treated, and potential hazard areas. If you see standing water, chances are it has mosquito larvae in it.

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