Black Vine Root Weevils
Little Notches
Every year my wife gets really excited when her Peonies start growing. Sometimes she calls me at work to tell me they have buds on them. Every year like clock work as soon as the leaves are out and growing, little notches along the edge of the leaves begin to show up. And the notches increase in number every day until every leaf has them.
The Black Vine Weevil
As its name suggests it is a Weevil. A Weevil is a flightless beetle with a snout like mouth part. Weevils are asexual which means they do not need a mate to reproduce. Black Vine Weevils will spend winter as an adult in any kind of leaf litter, mulch or thatch. When the ground temperatures begin to heat up the Black Vine Weevils will come out of dormancy and become active. The adult Black Vine Weevils will begin to lay eggs near plants under leaf litter or on the bark of a nearby shrub. In about two weeks the eggs will hatch out into larvae. These larvae will crawl down onto the soil and begin to eat on the plant roots. **Sounds familiar? Billbugs are also a weevils.** Usually the plants that the larvae are eating are big enough they wont cause serious damage.
Control
Control can begin early in the year as the ground temperatures begin to heat up and egg production increases. **Beneficial nematodes** can be inoculated into the soil to kill the larvae. Nematodes need to be applied to a wet soil, as they travel through water to find their host. Timing is very crucial for this type of application because if there is no host, the nematodes will quickly die. I had the chance to question a berry farmer in Oregon a few years ago on how he felt about nematodes.
“I saw some control but not total control of the weevil damage”
He allowed the extension agency to do a test on some of his vines. Their conclusion was that they needed to be put down earlier (timing).
Around the House
For the homeowner, we can use a product called Zamzows Tree and Shrub Systemic Insect Control. This is a liquid concentrate you spray on the foliage of the plant. The liquid is absorbed through the leaf and will protect the plant for up to four weeks. This will not do anything to the larvae in the soil but as I said, in our types of situations, they never reach such high populations that they damage plants too severely. Making sure you keep a clean environment around your plants is key. Clean up leaf litter and thatch in your grass if needed. Disturbing their hiding spots will force them to leave to find another place to hide during the day.
Susceptible Species
Personally, I find my peony and lilac experience the most foliage damage every year. Rhododendrons and azaleas can also be susceptible. Strawberry and veining berries will also have problems if there are high enough populations.
Conclusion
As I said earlier, the Black Vine Weevils damage is largely aesthetic. They rarely kill the plants. If you have lots of susceptible species planted together be sure to clean up around them every year. Spraying is a good way to keep the damage to a minimum. If you are having problems with larvae (which can be hard to diagnose) using nematodes early can control the populations from getting out of control.