If you've noticed scalloped notches along the edges of your yew, rhododendron, strawberry, or hosta leaves, root weevils are probably to blame. While the leaf damage looks alarming, it's the larvae feeding on roots underground that cause the real harm with their knock-on effects: stunted growth, chlorosis, wilting, and sometimes, plant death.
The good news: beneficial nematodes offer an effective, pesticide-free solution permitted for use by the City of Vancouver's bylaws. The catch is that they only work when applied at the right time, to the right soil conditions. This guide covers exactly what you need to do (before and after treatment) to get the best results.
The most common species in the Lower Mainland is the invasive Black Vine Weevil (Otiorhynchus sulcatus). Adults emerge at night in early summer and notch leaf edges; it's their larvae (grubs) that overwinter in the soil and feed on the absorbing roots and root crowns. A heavy infestation can kill established shrubs.
Beneficial nematodes are microscopic, naturally occurring roundworms found in healthy soil. The species often used for root weevil control, Steinernema kraussei (Sk) and H. bacteriophora (Hb), are harmless to people, pets, birds, bees, and earthworms. They seek out weevil larvae in the soil and kill them within a few days of contact.
No pesticides. No residue. No risk to pollinators.
Timing is the most important factor. Nematodes are only effective when soil temperature is consistently at or above the recommended soil temp and larvae are actively feeding near the surface.
| When | Nematode Type | Minimum Soil Temp | What's Happening |
| Mar - Apr | Sk | ≥ 5°C | 3rd generation larvae still vulnerable from overwintering |
| Aug - Sep | Hb | ≥ 10°C | Peak larval population; this is the most critical window |
The late-summer application is the one we prioritize most. Missing it means the larvae overwinter and emerge as adults the following spring.
Nematodes are not a knockdown spray. Results are gradual:
In moderate-to-heavy infestations, two consecutive years of treatment produce the best long-term results.
Yes. Beneficial nematodes are naturally occurring organisms found in healthy garden soil. They are not harmful to mammals, birds, bees, or earthworms. No protective gear or restricted access is required after treatment.
Light rain after application is actually helpful as it helps move nematodes into the soil. A heavy downpour immediately after may wash them away before they've had a chance to infiltrate. If very heavy rain is forecast, we may discuss rescheduling.
Yes, but the timing needs to line up. The Hb nematodes successfully attack those awful chafer grubs but chafer emerge slightly earlier than root weevil larvae in the season. If you have a chafer grub problem, make sure let us know so that we can properly adjust timing and dose for a better 2-in-1 treatment.
The clearest indicator is reduced leaf notching the following spring and summer. Because nematodes work underground, you won't see dead weevils, you'll simply notice less damage over time.
For mild cases this may not be necessary but for moderate to severe infestations we recommend this. Adult weevils lay eggs over an extended period in summer, so larvae hatch at different times. A spring and late-summer application covers both hatching periods and gives the best population knockdown.
Yes. Nematodes are available at select garden centres (ask for them at the desk as they require refrigeration). You can also order them online. The main challenge is timing, storage, and application conditions. Nematodes are living organisms that die quickly if exposed to heat, UV light, or dry soil. We handle the tricky part: product quality, soil temperature confirmation, and application timing.
Arbutus Tree Care offers root weevil assessment and nematode treatment for residential and commercial properties in Vancouver and the Lower Mainland. Contact us to schedule a site visit or discuss treatment timing for your property.