The Satin Moth and what you can do about it

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Many of the residents of Willow Park and Maple Ridge will have noticed a large number of distinctly white moths in the last month or so. These are called Satin Moths and due to a combination of environmental factors this season, their population has expanded and become more noticeable.

When feeding, the caterpillar of these moths can completely defoliate large mature trees of their leaves and can do this twice during the summer months. Because the caterpillar feed primarily on the poplar species of trees that are so prevalent in Willow Park and Maple Ridge, and repeated, severe defoliation over several seasons can lead to these trees dying, I have encouraged the Parks department to ramp up their current efforts to curb the increase in Satin Moth population. The Willow Ridge Community Association has also played a vital role in communicating this issue to me.

Information straight from The City's Parks department

The mature Satin Moth caterpillars grow to be 3.5 to 4.5 cm long, and are pale to medium grey-brown, with a darker head and back. Their backs are black with a central row of white or light yellow markings. They can be confused with the tent caterpillar which has a white strip down its back bordered by two blue lines. The adult moths have pure white wings with a satin-like lustre. They have a wingspan ranging from 3.5 to 5.0 cm and can be distinguished from other local white species by narrow alternating black and white bands on their legs.

The City's plan

Parks has been monitoring and tracking where large populations of the Satin Moth have appeared this year. The communities of Willow Park and Maple Ridge have specifically experienced larger insect populations. Over the next week, a non toxic sticky band will be applied to the base of poplar trees to trap newly hatched caterpillars as they make their way up the trunk of the trees into the canopy to feed. After assessment, Parks will start pressure spraying specific poplar trees with water in locations where the caterpillars are hatching and are present in large numbers. This will knock the egg masses and caterpillars out of the trees, preventing them from feeding on the tree's leaves.

Parks has consulted with The City of Edmonton on their experience with managing Satin Moth. A small parasitic wasp (Cotesia melanoscela) has established in Edmonton and for the most part now suppresses Satin Moth populations. This is typical in the natural environment where a pest will establish and the regulating predator is a few seasons behind. Once the predator is established it will keep the pest population in check. Parks is currently in the process of partnering with The City of Edmonton to collect the native parasitic wasp that attaches itself to the Satin Moth larva and kills it. These insects shall be released into locations with high populations of Satin Moth in an effort to "kick start" and establish a natural predator population.

Parks is also investigating other treatment options that would help to manage this pest. Application programs will be ready for early spring 2013 if high Satin Moth populations are present.

What can residents do for their trees?

Residents can help manage Satin Moth on their trees on their property. The greenish egg masses concentrated on the lower tree trunk can be scraped off with a dull blade and destroyed before they hatch. These eggs masses appear around mid-July. Also, a sticky band can be applied to the tree trunk during leaf out in May and again in July to catch overwintering and newly hatched caterpillars as they disperse into the canopy of the tree. These bands should be reapplied once they are saturated with the caterpillars and can be found at local garden centers. Also, residents can contact local landscape and tree care companies that provide Integrated Pest Management (IPM) services.

For more information, visit the Parks website. Should you have any comments or concerns, I can always be reached by phone at 403-268-1653 or contact my office​.​