Rocky View County Spruce Budworm
Monday, December 13, 2021
In the spring of 2021, Agricultural and Environmental Services hired a consultant to conduct a larval survey to better estimate the population density of spruce budworm in Bragg Creek and the surrounding area. Based on Provincial monitoring and Rocky View County’s survey numbers, the infestation was deemed to be moderate-severe in 2021. Leading up to 2021, the infestation had been categorized as light-moderate.
Pheromone-baited traps were placed to monitor adult moth numbers. The results from the pheromone traps show increased numbers outside the most severe infestation area. Further surveying will be required to determine where the eggs were laid and where spring feeding will occur.
A formal report (PDF, pg. 305) with management options for Rocky View County Council to consider was presented at the November 30, 2021, Council Meeting. A motion was passed directing Administration to continue monitoring and assessing the spruce budworm infestation in Bragg Creek and the surrounding area to determine if and when a more active management strategy becomes beneficial.
If you have any questions or concerns about this matter, please contact Rocky View County Agricultural Services at firstname.lastname@example.org or phone 403-230-1401.
Considerations for Management & Control
Spruce budworm is a native pest but considered destructive because they have eruptive phases. The first signs of larvae feeding (mining) on needles and buds are seen in early May as they feed on last year’s growth. Later in May and June, larvae are mining on newly developed needles and they complete their feeding in June.
Larvae of Western Spruce Budworm (Photo courtesy Natural Resource Canada, Canadian Forest Services)
Larvae of Eastern Spruce Budworm (Photo courtesy Natural Resource Canada, Canadian Forest Services)
Outbreaks occur approximately every 20 years and can last for several years. It is common to see outbreaks in over-mature spruce stands, as is the case in the Bragg Creek area. The population is generally kept in check by natural enemies and the variation in weather conditions. Weather events such as cold springs with late frosts and/or cold and wet summers can greatly reduce budworm populations.
It is important to note that spruce budworm damage will not kill trees in one season. Healthy, mature tree stands can withstand 5-7 years of consecutive severe defoliation while young trees may die after 4 consecutive severe years.
Short term impacts (<4 years) of an infestation include:
- Nuisance to residents due to the webbing and silk
- Reduced tree aesthetics due to foliage loss
Potential long-term impacts (4-10 years) include:
- Eventual tree mortality due to reduction in health and vigor
- Increased hazards to people, property & infrastructure
- Increased risks for wildfire spread
- Increased costs due to tree removal
Management Strategies for Residents
- If you are spraying your trees, do not use broad spectrum insecticides as they will kill the spruce budworm and many other beneficial insects, bacteria and viruses
- Use Bacillus thuringiensis var. kurstaki (Btk) that is readily available in local stores OR order in advance for next season. This natural biological insecticide is best to use in the early stages of larvae development.
- Timing is crucial when spraying – usually when bud caps come off and new needle growth begins
- Be prepared for next year’s larvae outbreak (mid May - end of June)
- Add bird feeders to attract spruce budworm predators
- Assess trees frequently and consider using a high-powered hose to spray down trees and knock larvae to the ground
- On small ornamental trees, vigorously shaking the tree may force the larvae to fall off
Tips for Boosting the Natural Immunity of your Trees
- Add arborist wood chips around trees to protect roots
- Adding between 4-6 inches of arborist wood chips helps keep moisture in the soil longer
- Regularly water your trees during drought (check your water for sodium levels), in late fall just before freezing and early in spring (especially if it is a dry spring).
- Provide fertilizers to roots from early spring until mid July to boost root system health.
- Do not remove any live branches as every needle counts for tree survival.
- Remove dead branches to reduce forest fire potential.
- Consider planting new trees (not just spruce) to diversify tree stand; planting a variety of trees and shrubs will create a more natural landscape.
- Make sure to monitor and assess for tree risk hazards such as falling trees.
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