Root Weevils

I didn’t even know what a root weevil was for all the years I was gardening at my last place which is in a mostly rural setting. But then, 18 months ago I had to move on short notice. So I packed up, picked up and dragged my mature 12 year old garden in the mucky weather of February and I managed to move it in less than two months! We now have a cute little house right in the middle of town.

Root WeevilLittle did I know that this new house is completely infested with weevils and ants for that matter but that’s a different story.

The weevils are inside the house and everywhere outside and they are devouring my garden like crazy! I’m not terribly impressed by this. (understatement!)

They love just about every plant I have. There are distinct notches out of so many leaves. The plants in my garden that are affected most are the blue blueberries but not the pink ones, garden phlox, strawberries, black mondo grass, oriental lilies, ferns, both my male and female kiwi vines. It’s crazy, they eat everything.

They are nocturnal, which means they hide in the daytime and come out at night to feast on your garden. You’ll need to go out at night with a flashlight to see them in action. You won’t see them in the daytime unless you have a very severe problem with them.

They’re called root weevils because the larva feed on the roots of the plants and then the adults emerge from the soil to devour the beautiful garden above ground. They aren’t easy to get rid of once they are in the garden but with some diligence it can be done. So, In order to fight this pest it’s very helpful to know a few facts about them and their behavior.

Weevil Damage on BlueberryIdentification

Root weevil adults will take notches out of the edges of your plants leaves. They do this repeatedly and can easily demolish entire leaves if they are left unattended. They will cause stress to the plant and destroy its beauty. These pictures are of two different blueberry plants in my garden. 

DescriptionWeevil Damage on Blueberry Leaves

They are black and look a bit like a rhino. Each one is very small and only about 1/4″ long. They do amazing amounts of damage for their size. They have wings under the hard black shell but they cannot fly. They walk quite slowly everywhere they go.

Life Cycle

All visible adults that you see are female. This is scary and it means that every single one of them have the ability to reproduce. The female emerges in late May through early July and then spends the entire summer eating your garden. She lays 300+ eggs on the soil as fall gets going. The larva hatch quickly, usually within two weeks and then tunnel into the soil and start their winter time feast on the roots of your plants. They stay deep in the soil and well protected all winter and then emerge again in May and then the cycle repeats.

Control and Eradication

Root weevils are very difficult to completely eradicate of once you have them, but it can be done with some effort over time. They tend to be worse in container gardens. There are some control measures that you can take which will help you deal with them and reduce their numbers a lot. With diligence over a few seasons, you might be able to get rid of them.

Hand Picking

Buy some big sheets of cardboard poster paper at the dollar store or use any cardboard you have around. The weevils feed at night so that’s when they are most active and present in the garden. This is the best time to hunt them.

Go out to the garden at night and use this paper under the plants. Set it under each of your plants on the ground or the top of the container and then shake the branches. The adults should drop off on to the paper. Use a bucket of soapy water to kill and dispose of the weevils.

Repeat this over a series of several nights until you don’t get any adults falling on to the paper when you shake the plant.

Daytime Hand Picking

Although the weevil is nocturnal you can still take steps towards getting rid of them in the daytime. Use more of the cardboard or poster paper and lay it on the ground around your plants and leave the paper there for the day. The weevils will hide under it and then will be on the other side of the paper when you pick it up. Dispose of them in the soapy bucket of water.

Make a spray bottle of dish soap and water solution and then saturate all of your plants with that, that will help slow down their progress too.


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Chemical Control

You may choose pesticide that has “Permethryn” in it such as this one, if you wish. This is a widely used pesticide for many different applications. It’s used for pest and insect control in the timber industry, the textile industry, the agriculture industry, for your pet’s health in fighting fleas and even in human health with getting rid of lice and scabies. IT’s a widely used clothing spray to kill and repel insects.

Permethryn has a wide variety of uses and has been deemed safe and effective for humans. It has also been labeled an essential medicine in a health system by the WHO (World Health Organization) (Source)

But…

Permethryn is also an indiscriminate insect killer.  This is why it has so many applications across so many industries. Indiscriminate means it kills everything. It kills the garden root weevils as well as all the bad bugs that interfere with our happy and healthy lives but it also kills all the good bugs that are essential and that we need to have around.

This includes our precious honey bees, ladybugs, lacewings, dragonflies, mason bees and many more. It also leeches into our water ways and harms aquatic life too. Basically, if a bug touches this liquid it dies, that’s it. That’s a pretty hefty price to pay. 

Nematodes

Using nematodes is a much more natural approach to killing the root weevils. The use of beneficial nematodes has been shown to be quite effective when used on this very destructive pest. Buy them here. The application method is different than standard pesticide use and the trick is applying it at exactly the right time of year so it’s most effective on the larva.

Water your garden and make sure the soil is pretty wet. The goal is to spray the nematodes as a drench to already moist soil and totally saturate the plant when the larva are present. The nematodes require water to be effective and travel through the soil. The application must happen when the temperature is above 60 degrees F.

You may need to do this several times to get them under good control. Use a backpack sprayer or hose end sprayer if you are dealing with large plants or trees.

Tanglefoot

This product can be used in conjunction with the other methods to help fight the root weevils as well. This may or may not be reasonable depending on the types of plants you have. Tanglefoot is difficult to use on shrubs or plants with many branches, so it’s best on trees and plants with a single stalk or only a few stalks. It’s best to wrap the tree trunk in plastic and then use Tanglefoot (please read here if you are unfamiliar with Tanglefoot). Applying this correctly will help trap the adult females that are walking around devouring your garden. 


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One thought on “Root Weevils

  1. Gramma Jo

    May 10, 2018 at 11:27am

    In April/May, I also dig through the soil and squish all the white grubs I can find, and by then some are even pupating. The dirt falls away from them, and if they are any size at all, they are bright white, so not too difficult to see. Every one I squish, I think “now THAT one won’t lay 300 eggs this summer!” A white sheet, placed in folds around the base of the plant, also traps them overnight. In the morning, open up the sheet and squish the adults or place in soapy water.

    I agree, they are a terrible pest and nearly impossible to eradicate. They don’t eat wheat, but who wants to grow wheat! They eat everything else.

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    • Author

      Stacy

      May 11, 2018 at 6:12am

      Thank you for the great information! I wasn’t aware of the folded sheet method to trap them.
      You’re so right, they multiply really fast and cause real problems to everything worth growing.

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